• The interannual (2-7 year band) precipitation in Southern California is closely related to ENSO... more • The interannual (2-7 year band) precipitation in Southern California is closely related to ENSO variance originating from the tropical Pacific. • Extratropical pressure systems modulate the interannual precipitation changes in Southern California by influencing the ENSO teleconnection. • The magnitude and frequency of interannual precipitation variance in Southern California changes throughout the past 2000 years.
Proceedings of the Ocean Drilling Program, 145 Scientific Results, 1995
The climatic change from early Eocene warmth to the onset of Oligocene continental glaciation may... more The climatic change from early Eocene warmth to the onset of Oligocene continental glaciation may have been associated with changes in deep-water circulation. The North Pacific Transect (Ocean Drilling Program Leg 145) recovered Paleogene carbonates at Site 883 (2000 m paleodepth; upper Paleocene to lower Oligocene) and Site 884 (3300 m paleodepth; lower Eocene to lower Oligocene), providing a middle and upper Eocene isotope record from the North Pacific. These new data, combined with existing data from Site 577, allow the construction of a late Paleocene and Eocene composite Pacific isotopic record. Interbasinal isotopic comparisons indicate that during the early middle to middle middle Eocene (ca. 51-46 Ma) the Southern Ocean was the sole source of deep water to the North Pacific. However, during the early Eocene (ca. 57-52 Ma) and the middle middle Eocene to Oligocene (ca. 46-36 Ma), there were two sources of deep water: a cool, nutrient-depleted source originating in the Southern Ocean and a warmer, more nutrient-enriched source probably originating in mid-latitudes. Deep-water circulation changes have the potential to profoundly affect benthic foraminifer communities. During the early Eocene, the deep Site 884 was characterized by a distinct abyssal (>3000 m) agglutinated foraminiferal faunal assemblage. The abyssal assemblage disappeared near the early/middle Eocene boundary, coinciding with both the first Cenozoic deep-water cooling step and an inferred shift in circulation from a two-source to a one-source mode. We suggest that benthic foraminifer assemblages responded to both rapid cooling and decreased corrosivity as the circulation regime shifted from one mode to another.
Proceedings of the Ocean Drilling Program, 150X Scientific Results, 1997
Stratigraphic correlation between shallow-water and deep-sea sections has proven notoriously diff... more Stratigraphic correlation between shallow-water and deep-sea sections has proven notoriously difficult because of hiatuses, diachrony of marker species, and diagenesis on the shelf. Isotope stratigraphy, biostratigraphy, and magnetostratigraphy reveal that sedimentation on the New Jersey Margin (Island Beach borehole) was relatively continuous during the late Paleocene and early Eocene (~58−52.5 Ma). All planktonic foraminiferal and calcareous nannofossil zones are represented at Island Beach. However, two disconformities are recognized in the upper Paleocene to lower Eocene section: a physical surface (lithologic change) at the Vincentown/Manasquan contact (uppermost Paleocene), which has a hiatus of ~0.3 m.y., and a ~0.4-m.y. gap associated with a paraconformity in the lower Eocene section. Stable isotopic data from the New Jersey Margin indicate that this neritic section can be successfully correlated to the deep sea using δ 13 C and δ 18 O of benthic foraminiferal calcite. Comparison between the Island Beach and global isotopic records (as represented by deep Pacific Site 577) shows that Island Beach parallels the global trend in both δ 18 O and δ 13 C. All major features of the late Paleocene to early Eocene global isotopic record are preserved, including general δ 18 O decrease, step-like δ 13 C decrease, and the well-known latest Paleocene δ 13 C excursion. We recognize three 1-to 1.5-m.y. δ 13 C steps over our interval of study at both Island Beach and the deep Pacific (~56.6−55.8 Ma; ~55.5−54 Ma; ~53.6−52.6 Ma). These steps are correlative with intervals of increased paleodepth, as indicated by benthic foraminiferal biofacies studies, and decreased δ 18 O values. We suggest a link between increased temperature and sea level, and reduced organic carbon burial in the deep sea. Previous workers identified a latest Paleocene benthic foraminiferal faunal change on the New Jersey Margin (Clayton borehole). They suggested that this faunal turnover was the neritic correlative of the well-known latest Paleocene benthic extinction event. Our data indicate that at Island Beach, uppermost Paleocene δ 13 C and δ 18 O excursions occur above the disconformity and the associated shallow-water benthic foraminiferal faunal change. This isotopic excursion may be synchronous with the deep-sea extinction event or with a younger δ 13 C decrease. We suggest that the benthic foraminiferal event on the New Jersey Margin was the result of a dramatic water-depth increase on the shelf and was unrelated to the deep-sea extinction.
Proceedings of the Ocean Drilling Program, 150X Scientific Results, 1997
Boreholes from Island Beach, Allaire, Atlantic City, and Mays Landing, NJ provide an excellent ch... more Boreholes from Island Beach, Allaire, Atlantic City, and Mays Landing, NJ provide an excellent chronology of lower to middle Eocene passive margin sequences and allow analysis of long-term sea-level changes and sedimentation patterns. These New Jersey sequences are tied directly to the geomagnetic polarity time scale through magnetostratigraphy. Integrated stratigraphy (including magnetostratigraphy, lithostratigraphy, plankton biostratigraphy, and benthic foraminiferal biofacies studies) reveals that these sections contain a relatively continuous record of lowermost Eocene to middle Eocene deposition interrupted by short hiatuses. A sequence boundary at the base of the section spans the Paleocene/Eocene boundary, representing a hiatus from 55.8 to 54.7 Ma. A second sequence boundary is associated with a hiatus from 54.0 to 53.4 Ma. A third sequence boundary is associated with a hiatus from 52.9 to 52.3 Ma. Two major unconformities occur near the lower/middle Eocene boundary at all three boreholes. The first represents a hiatus between 50.9 and ~50.5 to 49.9 Ma; the second, between ~49.6 and 48.6 Ma. Early Eocene water depths inferred from benthic foraminiferal biofacies analysis varied from 150 to 200 m and reached their maximum depth between 53.4 and 53.2 Ma. In the middle Eocene, the sedimentation record is less continuous with hiatuses from 48.3 to 47.9 Ma, 46.9 to 44.5 Ma, and 43.4 to ~41.2 Ma. A major lithofacies change from carbonate dominated to siliciclastic dominated occurred by 41.2 Ma. Of the 14 sequences inferred by Exxon for the early to middle Eocene, nine are resolvable on the New Jersey Margin and the remaining five appear to be combined with others. Thus the New Jersey record is consistent with the Exxon record for the early to middle Eocene, although the New Jersey record is better dated. Comparison of the record of sedimentation with the global δ 18 O record shows interesting parallels. It is unlikely that early Eocene sequence boundaries are the result of glacioeustasy because hiatuses from the New Jersey Coastal Plain in this interval do not match increases in the δ 18 O record. In the late middle Eocene, concomitant increases in the planktonic and benthic δ 18 O records coincide with the timing of hiatuses on the New Jersey Coastal Plain. Increases in the δ 18 O records between 43 and 41 Ma coincide with a New Jersey hiatus and a corresponding change in sedimentation type from carbonate dominated to siliciclastic dominated. We conclude that these represent evidence of the first Antarctic ice cap and the beginning of the "Icehouse" world.
Proceedings of the National Academy of Sciences, 2016
Significance Despite numerous publications reporting the accumulation of petroleum hydrocarbons a... more Significance Despite numerous publications reporting the accumulation of petroleum hydrocarbons associated with the Deepwater Horizon spill on the seafloor, the mechanisms of their delivery to the seafloor remain unclear. We demonstrate sedimentation of black carbon derived from the in situ burning of surface oil slicks for about 2 mo following the cessation of burning while other contaminants from the spill, including bioactive barium derived from drilling mud, continued to sediment for at least 5 mo after the well was capped. We also show that the episodic sinking of spill-associated substances was mainly mediated by marine particles, especially diatoms. Together, these data demonstrate delivery mechanisms of contaminants from the spill to benthic ecosystems in the deep Gulf of Mexico.
ABSTRACT Santa Barbara Basin is well known for producing high quality paleoclimate reconstruction... more ABSTRACT Santa Barbara Basin is well known for producing high quality paleoclimate reconstructions, however the validity of correlations between climate change recorded in the basin and other regions rests upon the accuracy of age models. Two independent well established chronologies based on varve counting and radiocarbon dates do not agree over the last 2 millennia. Here we test the validity of two assumptions associated with the two chronologies: 1) The regional reservoir age of marine surface waters 641±119 years) does not vary through time; and 2) laminae couplets preserved in basin sediments are annual and counted with high precision. In this high-resolution 14C study of SBB sediments we compare 49 mixed planktonic foraminifer and 21 terrestrial organic carbon 14C dates to the varve chronology, to extend the high-resolution paleoclimate chronology of the basin back ~2,000 years. We show evidence that both assumptions may be incorrect. First, regional reservoir ages appear to fluctuate through time, varying between 525-750 years (ΔR = 125-350 year). Second, an apparent consistent (r2 = 0.95) undercounting of varves occurs between ~1700 and 400 AD based on a new varying ΔR 14C chronology, therefore suggesting that some laminae couplets may not be annual. However, the consistency of the offset between the two chronologies suggests that a correction can be applied to the lamination counts to account for missing years. As the variable reservoir ages determined by comparison of planktonic foraminiferal radiocarbon with terrestrial 14C are not observed in benthic-planktonic paired 14C differences, we suggest they reflect changes in the reservoir age of the upper (500 m) water column on the North American margin. Diffusion of young atmospheric carbon into the upper water column may be enhanced ~1400 years BP due to stronger winds or reduced sea ice cover in the North Pacific. Alternately diffusion of old oceanic carbon from deep water masses might be enhanced ~500 years BP by changes in meridional overturning circulation.
Eos, Transactions American Geophysical Union, 2006
A fundamental goal of Earth science is to understand the remarkable instability of late Quaternar... more A fundamental goal of Earth science is to understand the remarkable instability of late Quaternary global climate prior to the begin ning of the Holocene, about 11,000 years ago. This unusual climate behavior was charac terized by millennial-scale climate oscillations on suborbital timescales, and a distinctive 'sawtooth' pattern of very abrupt glacial and stadial terminations (within decades) followed by more gradual global cooling [e.g., Dansgaard et al, 1993; Hendy and Kennett, 1999]. The fact that both major (glacial) and minor (stadial) cooling periods in Earth's climate were terminated by similar abrupt warming episodes suggests a common mechanism driving such rapid changes in global climate. Understanding the causes of this instability is crucial given developing concerns about global warming, yet knowledge about this climate behavior has been essentially con fined to the last 150,000 years or so, owing to the absence of available sequences of suffi cient age and chronological resolution. The high-resolution paleoclimate record from the Greenland ice cores is limited to about 110 thousand years ago (ka),and although Ant arctic ice cores now extend back to more than 740 ka [European Project for Ice Coring in Antarctica, 2004], these latter cores primar ily provide information about high-latitude conditions at much lower resolution than is required to address abrupt climate change. Longer high-resolution paleoclimate records are thus essential to understanding the natural mechanisms of global climate change. Ideally, such records should repre sent changes in both the atmosphere and oceans, and at low, middle, and high latitude sites. For this reason, high-resolution paleocli mate records extracted from marine sedi ment cores are of critical importance. Ocean Drilling Program (ODP) Site 893, located in Santa Barbara Basin (Figure l),is one of the few high-fidelity, continuous climate
We present records of the marine environmental change that occurred as regional climate shifted f... more We present records of the marine environmental change that occurred as regional climate shifted from the Medieval Climate Anomaly (MCA) into the Little Ice Age (LIA) based on planktonic foraminiferal and diatom assemblages alongside geochemical evidence of surface water temperature and salinity change from Santa Barbara Basin (SBB). The present climate reconstructions available in SBB clearly demonstrate that ocean and
Lithologic, faunal, seismic, and isotopic evidence from the Blake Nose (subtropical western North... more Lithologic, faunal, seismic, and isotopic evidence from the Blake Nose (subtropical western North Atlantic) links a massive release of biogenic methane ∼55.5 million years ago to a warming of deep-ocean and high-latitude surface waters, a large perturbation in the combined ocean-atmosphere carbon cycle (the largest of the past 90 million years), a mass extinction event in benthic faunas, and a radiation of mammalian orders. The deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming, massive carbon input to the global exogenic carbon cycle, pelagic carbonate dissolution, a decrease in dissolved oxygen, and a benthic foraminiferal extinction event. These events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the Blake Nose as a site of methane release.
Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstr... more Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8° ± 0.7°C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5°C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.
A high-resolution western tropical Atlantic sea surface temperature (SST) record from the Cariaco... more A high-resolution western tropical Atlantic sea surface temperature (SST) record from the Cariaco Basin on the northern Venezuelan shelf, based on Mg/Ca values in surface-dwelling planktonic foraminifera, reveals that changes in SST over the last glacial termination are synchronous, within ±30 to ±90 years, with the Greenland Ice Sheet Project 2 air temperature proxy record and atmospheric methane record. The most prominent deglacial event in the Cariaco record occurred during the Younger Dryas time interval, when SSTs dropped by 3° to 4°C. A rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature, atmospheric methane, and high-latitude changes during the Younger Dryas.
Records of planktonic and benthic foraminiferal d 18 O and planktonic Mg/Ca from core TR163-22, j... more Records of planktonic and benthic foraminiferal d 18 O and planktonic Mg/Ca from core TR163-22, just northwest of the Gala´pagos Islands, reveal a detailed (250-450 year resolution) climate history of the region over the last 135 thousand years (kyr). Sea surface temperatures (SSTs), reconstructed from G. ruber Mg/Ca, averaged 24.370.4 1C during the Holocene, 22.670.6 1C during marine isotope stage (MIS) 2, 3 and 4, and 26.070.9 1C during MIS 5e. Changes in SST lead changes in both planktonic and benthic d 18 O by an average $3 kyr, suggesting that SST changes in this region predated continental ice volume changes. Changes in SST display clear millennial scale variability, especially in marine isotope stage 3, with behavior somewhat similar to Antarctic proxy air temperature and South Pacific SST records. Removal of the temperature component from the planktonic d 18 O record demonstrates that glacialinterglacial d 18 O-water changes at this site were 1.070.2%, similar to estimates for mean ocean shifts, implying that salinity changes due to regional hydrological variation between the Last Glacial Maximum and Holocene in the Gala´pagos region were minimal. Comparison between the TR163-22 SST record and an SST record from core TR163-19 North of the Equatorial Front reveals a largely similar broadscale climate history, suggesting that changes in the Gala´pagos region were caused by large scale forcing rather than by local or regional dynamical changes. Changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large-scale climate changes in the eastern equatorial Pacific.
ABSTRACT Santa Barbara Basin (SBB) is well known for producing high quality paleoclimate reconstr... more ABSTRACT Santa Barbara Basin (SBB) is well known for producing high quality paleoclimate reconstructions, but the validity of correlations between the basin and other regions rests upon age model accuracy. Yet, the two independent and well-established chronologies based on varve counting and radiocarbon dating do not consistently agree during the last two millennia. Here the validity of age model assumptions is tested including whether 1) the regional reservoir age of surface waters was invariably 641 ± 119 years through time, and/or 2) SBB laminae couplets are consistently annual varves and counted with sufficient precision. This high-resolution 14C study of SBB sediments compares 49 mixed planktonic foraminiferal carbonate and 20 terrestrial organic carbon 14C dates to the varve chronology, to extend the high-resolution paleoclimate chronology of the basin back ∼2000 years. Evidence indicates that regional reservoir ages do not remain constant through time with ΔR, (i.e. regional reservoir age minus variations in the global mixed-layer ocean reservoir age) fluctuating between 80 and 350 years. Second, there is a consistent (R2 = 0.96) undercounting of the varves between 150 and ∼1700 AD based on a new varying ΔR 14C chronology, indicating that some laminae couplets may not be annual. Loss of varves may occur when low riverine input and infrequent winter storm activity during drought intervals fail to supply a siliciclastic layer.
The relationship between water column processes and sedimentation was investigated using a five y... more The relationship between water column processes and sedimentation was investigated using a five year time series of biweekly water column measurements and continuous sediment trap collections in the Santa Barbara Basin, California. Conditions during the strong El Niño period of 1997-98 were compared to those during the previous years and the post El Niño period. Suspended particulate concentrations of chlorophyll a (chl a), particulate organic carbon (POC), particulate organic nitrogen (PON) and biogenic silica (bSi) normally underwent a seasonal cycle characterized by high phytoplankton abundance in the spring, dominated by diatoms, followed by lower concentrations of biogenic particles throughout the rest of the year. Maxima in sinking fluxes of POC, PON, bSi and lithogenic silica (lSi) generally occurred during the summer. Prior to the El Niño period, molar ratios of C/N, Si/C and Si/N were all higher in sinking particulate material relative to particulate material suspended in the upper 75 m. Si/N and Si/C ratios were highest in the spring and summer in both surface and sinking pools. During the 1997-98 El Niño, the seasonal evolution of the density structure of surface waters was altered by the presence of a water mass high in temperature and low in salinity. The depression of the thermocline resulted in concentrations of nitrate, phosphate and silicic acid in the upper 75 m becoming lower that those measured in other years. Mean chl a and bSi concentrations integrated from the surface to 75 m were low on an annual basis, but there were no clear changes in the seasonality of suspended particle concentrations. Perhaps unexpectedly, fluxes of POC, PON and lSi at 470 m increased during the El Niño period. Lower C/N ratios and shorter turnover times suggest increases in the export ratios of POC and PON at that time. We hypothesize that the increase in lSi flux, despite the absence of elevated concentrations of lSi in the upper 75 m, resulted from the lateral advection of particles into the region from the increased riverine discharges at the margins of the basin and subsequent scavenging of the small particles by organic material. Decreases in ratios of C/N, Si/C and Si/N in sinking particles that occurred during the El Niño were sustained until the end of the time series in June 1999, and may have resulted from a shift toward a less diatom dominated pool of sinking particles.
A new centennial-scale Mg/Ca temperature record from the California margin (ODP Site 1017E) revea... more A new centennial-scale Mg/Ca temperature record from the California margin (ODP Site 1017E) reveals large millennial-scale oscillations between 10 to 60 kyr. This record indicates that sea surface temperature on the California Margin warmed rapidly on the deglacial by 7.4 AE 0.8 C, and was preceded by a pre-Bølling temperature oscillation of 2.6 AE 1.2 C. Millennial-scale events of the last glacial episode were marked by sea surface temperature oscillations of between 3 and 7 C on the California margin, and interstadials were associated with an increase in surface water salinity. The data are consistent with evidence for a glacial southward shift in the polar jet stream and concomitant strengthening of the relatively cold, fresh California Current during stadial events. The data also support previous hypotheses suggesting a tight coupling between the North Atlantic and northeast Pacific response to climate instability of the last glacial episode.
Oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate ... more Oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions, with those of benthic foraminifera providing information on the deep oceans. Reconstructions are complicated by interspecies isotopic offsets that result from microhabitat preferences (carbonate precipitation in isotopically distinct environments) and vital effects (species-specific metabolic variation in isotopic fractionation). We provide correction factors for early Cenozoic benthic foraminifera commonly used for isotopic measurements (Cibicidoides spp., Nuttallides truempyi, Oridorsalis spp., Stensioina beccariiformis, Hanzawaia ammophila, and Bulimina spp.), showing that most yield reliable isotopic proxies of environmental change. The statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies. Interspecies isotopic offsets appear to have changed through the Cenozoic, either (1) as a result of evolutionary changes or (2) as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies. Regardless of the reason, the assumption that isotopic offsets have remained constant through the Cenozoic has introduced an $1-2°C uncertainty into deep sea paleotemperature calculations. In addition, we compare multiple species isotopic data from a western North Atlantic section that includes the Paleocene-Eocene thermal maximum to determine the most reliable isotopic indicator for this event. We propose that Oridorsalis spp. was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time; it may be the best recorder at other locations and for other extreme events also.
We have developed cold-end Mg/Ca-temperature calibrations for three common Arctic benthic foramin... more We have developed cold-end Mg/Ca-temperature calibrations for three common Arctic benthic foraminifera, Islandiella norcrossi/helenae, Melonis barleeanus, and Cassidulina neoteretis, and compare the three calibrations in a late Holocene downcore record (0-4000 cal yr B.P.). The calibration and downcore trends for the three Arctic species extend the observation that Mg incorporation into benthic foraminifera is species specific. For the calibration we use a set of CTD casts, bottom water d 18 O seawater measurements, and surface grab-samples collected from the Iceland margin (cruise B997) and the Greenland margin (cruise BS1191). Water depth of sites used ranges from 165 to 656 m, while spatial bottom temperature ranges from 0 to 7°C. Mg/Ca values ranged from 1.02 to 1.47 for I. norcrossi/helenae, 0.64 to 2.21 for M. barleeanus, and 0.93 to 1.38 mmol/mol for C. neoteretis. We calibrated Mg/Ca content against isotopic calcification temperature (calculated using T = 16.9 À 4.0*(d 18 O calcite corrected for vital effect À d 18 O seawater)). Exponential calibrations for the three species are as follows: I. norcrossi/helenae Mg/Ca = 1.051 ± 0.03 * exp(0.060 ± 0.011 * T), M. barleeanus Mg/Ca = 0.658 ± 0.07 * exp(0.137 ± 0.020 * T), and C. neoteretis Mg/Ca = 0.864 ± 0.07 * exp(0.082 ± 0.020 * T). On the basis of Mg/Ca in these benthic species the downcore record from core MD99-2269 is reconstructed. Bottom temperature values are interpreted to reflect variable inflow of Atlantic and Arctic water to the north Iceland shelf during the last 4000 cal yr B.P. All three reconstructions show a decline by 0.1°C per century from circa 1500-0 cal yr B.P., which coincides with an increase in Arctic benthic foraminifera abundances and a rise in sea ice proxies in the same core. Intriguingly, C. neoteretis diverges periodically to higher average temperature (Atlantic water conditions) than shown by M. barleeanus or I. norcrossi/helenae (which both show Arctic water temperature) circa 1500-4000 cal yr B.P.
Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca a... more Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca and Sr/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg/Ca and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of ±0.2°C and ±0.5°C, respectively. The analysis of foraminifera suggests an interlaboratory variance of about ±8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about ±2-3°C. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about ±1-2°C) and a bias (about 1°C) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.
• The interannual (2-7 year band) precipitation in Southern California is closely related to ENSO... more • The interannual (2-7 year band) precipitation in Southern California is closely related to ENSO variance originating from the tropical Pacific. • Extratropical pressure systems modulate the interannual precipitation changes in Southern California by influencing the ENSO teleconnection. • The magnitude and frequency of interannual precipitation variance in Southern California changes throughout the past 2000 years.
Proceedings of the Ocean Drilling Program, 145 Scientific Results, 1995
The climatic change from early Eocene warmth to the onset of Oligocene continental glaciation may... more The climatic change from early Eocene warmth to the onset of Oligocene continental glaciation may have been associated with changes in deep-water circulation. The North Pacific Transect (Ocean Drilling Program Leg 145) recovered Paleogene carbonates at Site 883 (2000 m paleodepth; upper Paleocene to lower Oligocene) and Site 884 (3300 m paleodepth; lower Eocene to lower Oligocene), providing a middle and upper Eocene isotope record from the North Pacific. These new data, combined with existing data from Site 577, allow the construction of a late Paleocene and Eocene composite Pacific isotopic record. Interbasinal isotopic comparisons indicate that during the early middle to middle middle Eocene (ca. 51-46 Ma) the Southern Ocean was the sole source of deep water to the North Pacific. However, during the early Eocene (ca. 57-52 Ma) and the middle middle Eocene to Oligocene (ca. 46-36 Ma), there were two sources of deep water: a cool, nutrient-depleted source originating in the Southern Ocean and a warmer, more nutrient-enriched source probably originating in mid-latitudes. Deep-water circulation changes have the potential to profoundly affect benthic foraminifer communities. During the early Eocene, the deep Site 884 was characterized by a distinct abyssal (>3000 m) agglutinated foraminiferal faunal assemblage. The abyssal assemblage disappeared near the early/middle Eocene boundary, coinciding with both the first Cenozoic deep-water cooling step and an inferred shift in circulation from a two-source to a one-source mode. We suggest that benthic foraminifer assemblages responded to both rapid cooling and decreased corrosivity as the circulation regime shifted from one mode to another.
Proceedings of the Ocean Drilling Program, 150X Scientific Results, 1997
Stratigraphic correlation between shallow-water and deep-sea sections has proven notoriously diff... more Stratigraphic correlation between shallow-water and deep-sea sections has proven notoriously difficult because of hiatuses, diachrony of marker species, and diagenesis on the shelf. Isotope stratigraphy, biostratigraphy, and magnetostratigraphy reveal that sedimentation on the New Jersey Margin (Island Beach borehole) was relatively continuous during the late Paleocene and early Eocene (~58−52.5 Ma). All planktonic foraminiferal and calcareous nannofossil zones are represented at Island Beach. However, two disconformities are recognized in the upper Paleocene to lower Eocene section: a physical surface (lithologic change) at the Vincentown/Manasquan contact (uppermost Paleocene), which has a hiatus of ~0.3 m.y., and a ~0.4-m.y. gap associated with a paraconformity in the lower Eocene section. Stable isotopic data from the New Jersey Margin indicate that this neritic section can be successfully correlated to the deep sea using δ 13 C and δ 18 O of benthic foraminiferal calcite. Comparison between the Island Beach and global isotopic records (as represented by deep Pacific Site 577) shows that Island Beach parallels the global trend in both δ 18 O and δ 13 C. All major features of the late Paleocene to early Eocene global isotopic record are preserved, including general δ 18 O decrease, step-like δ 13 C decrease, and the well-known latest Paleocene δ 13 C excursion. We recognize three 1-to 1.5-m.y. δ 13 C steps over our interval of study at both Island Beach and the deep Pacific (~56.6−55.8 Ma; ~55.5−54 Ma; ~53.6−52.6 Ma). These steps are correlative with intervals of increased paleodepth, as indicated by benthic foraminiferal biofacies studies, and decreased δ 18 O values. We suggest a link between increased temperature and sea level, and reduced organic carbon burial in the deep sea. Previous workers identified a latest Paleocene benthic foraminiferal faunal change on the New Jersey Margin (Clayton borehole). They suggested that this faunal turnover was the neritic correlative of the well-known latest Paleocene benthic extinction event. Our data indicate that at Island Beach, uppermost Paleocene δ 13 C and δ 18 O excursions occur above the disconformity and the associated shallow-water benthic foraminiferal faunal change. This isotopic excursion may be synchronous with the deep-sea extinction event or with a younger δ 13 C decrease. We suggest that the benthic foraminiferal event on the New Jersey Margin was the result of a dramatic water-depth increase on the shelf and was unrelated to the deep-sea extinction.
Proceedings of the Ocean Drilling Program, 150X Scientific Results, 1997
Boreholes from Island Beach, Allaire, Atlantic City, and Mays Landing, NJ provide an excellent ch... more Boreholes from Island Beach, Allaire, Atlantic City, and Mays Landing, NJ provide an excellent chronology of lower to middle Eocene passive margin sequences and allow analysis of long-term sea-level changes and sedimentation patterns. These New Jersey sequences are tied directly to the geomagnetic polarity time scale through magnetostratigraphy. Integrated stratigraphy (including magnetostratigraphy, lithostratigraphy, plankton biostratigraphy, and benthic foraminiferal biofacies studies) reveals that these sections contain a relatively continuous record of lowermost Eocene to middle Eocene deposition interrupted by short hiatuses. A sequence boundary at the base of the section spans the Paleocene/Eocene boundary, representing a hiatus from 55.8 to 54.7 Ma. A second sequence boundary is associated with a hiatus from 54.0 to 53.4 Ma. A third sequence boundary is associated with a hiatus from 52.9 to 52.3 Ma. Two major unconformities occur near the lower/middle Eocene boundary at all three boreholes. The first represents a hiatus between 50.9 and ~50.5 to 49.9 Ma; the second, between ~49.6 and 48.6 Ma. Early Eocene water depths inferred from benthic foraminiferal biofacies analysis varied from 150 to 200 m and reached their maximum depth between 53.4 and 53.2 Ma. In the middle Eocene, the sedimentation record is less continuous with hiatuses from 48.3 to 47.9 Ma, 46.9 to 44.5 Ma, and 43.4 to ~41.2 Ma. A major lithofacies change from carbonate dominated to siliciclastic dominated occurred by 41.2 Ma. Of the 14 sequences inferred by Exxon for the early to middle Eocene, nine are resolvable on the New Jersey Margin and the remaining five appear to be combined with others. Thus the New Jersey record is consistent with the Exxon record for the early to middle Eocene, although the New Jersey record is better dated. Comparison of the record of sedimentation with the global δ 18 O record shows interesting parallels. It is unlikely that early Eocene sequence boundaries are the result of glacioeustasy because hiatuses from the New Jersey Coastal Plain in this interval do not match increases in the δ 18 O record. In the late middle Eocene, concomitant increases in the planktonic and benthic δ 18 O records coincide with the timing of hiatuses on the New Jersey Coastal Plain. Increases in the δ 18 O records between 43 and 41 Ma coincide with a New Jersey hiatus and a corresponding change in sedimentation type from carbonate dominated to siliciclastic dominated. We conclude that these represent evidence of the first Antarctic ice cap and the beginning of the "Icehouse" world.
Proceedings of the National Academy of Sciences, 2016
Significance Despite numerous publications reporting the accumulation of petroleum hydrocarbons a... more Significance Despite numerous publications reporting the accumulation of petroleum hydrocarbons associated with the Deepwater Horizon spill on the seafloor, the mechanisms of their delivery to the seafloor remain unclear. We demonstrate sedimentation of black carbon derived from the in situ burning of surface oil slicks for about 2 mo following the cessation of burning while other contaminants from the spill, including bioactive barium derived from drilling mud, continued to sediment for at least 5 mo after the well was capped. We also show that the episodic sinking of spill-associated substances was mainly mediated by marine particles, especially diatoms. Together, these data demonstrate delivery mechanisms of contaminants from the spill to benthic ecosystems in the deep Gulf of Mexico.
ABSTRACT Santa Barbara Basin is well known for producing high quality paleoclimate reconstruction... more ABSTRACT Santa Barbara Basin is well known for producing high quality paleoclimate reconstructions, however the validity of correlations between climate change recorded in the basin and other regions rests upon the accuracy of age models. Two independent well established chronologies based on varve counting and radiocarbon dates do not agree over the last 2 millennia. Here we test the validity of two assumptions associated with the two chronologies: 1) The regional reservoir age of marine surface waters 641±119 years) does not vary through time; and 2) laminae couplets preserved in basin sediments are annual and counted with high precision. In this high-resolution 14C study of SBB sediments we compare 49 mixed planktonic foraminifer and 21 terrestrial organic carbon 14C dates to the varve chronology, to extend the high-resolution paleoclimate chronology of the basin back ~2,000 years. We show evidence that both assumptions may be incorrect. First, regional reservoir ages appear to fluctuate through time, varying between 525-750 years (ΔR = 125-350 year). Second, an apparent consistent (r2 = 0.95) undercounting of varves occurs between ~1700 and 400 AD based on a new varying ΔR 14C chronology, therefore suggesting that some laminae couplets may not be annual. However, the consistency of the offset between the two chronologies suggests that a correction can be applied to the lamination counts to account for missing years. As the variable reservoir ages determined by comparison of planktonic foraminiferal radiocarbon with terrestrial 14C are not observed in benthic-planktonic paired 14C differences, we suggest they reflect changes in the reservoir age of the upper (500 m) water column on the North American margin. Diffusion of young atmospheric carbon into the upper water column may be enhanced ~1400 years BP due to stronger winds or reduced sea ice cover in the North Pacific. Alternately diffusion of old oceanic carbon from deep water masses might be enhanced ~500 years BP by changes in meridional overturning circulation.
Eos, Transactions American Geophysical Union, 2006
A fundamental goal of Earth science is to understand the remarkable instability of late Quaternar... more A fundamental goal of Earth science is to understand the remarkable instability of late Quaternary global climate prior to the begin ning of the Holocene, about 11,000 years ago. This unusual climate behavior was charac terized by millennial-scale climate oscillations on suborbital timescales, and a distinctive 'sawtooth' pattern of very abrupt glacial and stadial terminations (within decades) followed by more gradual global cooling [e.g., Dansgaard et al, 1993; Hendy and Kennett, 1999]. The fact that both major (glacial) and minor (stadial) cooling periods in Earth's climate were terminated by similar abrupt warming episodes suggests a common mechanism driving such rapid changes in global climate. Understanding the causes of this instability is crucial given developing concerns about global warming, yet knowledge about this climate behavior has been essentially con fined to the last 150,000 years or so, owing to the absence of available sequences of suffi cient age and chronological resolution. The high-resolution paleoclimate record from the Greenland ice cores is limited to about 110 thousand years ago (ka),and although Ant arctic ice cores now extend back to more than 740 ka [European Project for Ice Coring in Antarctica, 2004], these latter cores primar ily provide information about high-latitude conditions at much lower resolution than is required to address abrupt climate change. Longer high-resolution paleoclimate records are thus essential to understanding the natural mechanisms of global climate change. Ideally, such records should repre sent changes in both the atmosphere and oceans, and at low, middle, and high latitude sites. For this reason, high-resolution paleocli mate records extracted from marine sedi ment cores are of critical importance. Ocean Drilling Program (ODP) Site 893, located in Santa Barbara Basin (Figure l),is one of the few high-fidelity, continuous climate
We present records of the marine environmental change that occurred as regional climate shifted f... more We present records of the marine environmental change that occurred as regional climate shifted from the Medieval Climate Anomaly (MCA) into the Little Ice Age (LIA) based on planktonic foraminiferal and diatom assemblages alongside geochemical evidence of surface water temperature and salinity change from Santa Barbara Basin (SBB). The present climate reconstructions available in SBB clearly demonstrate that ocean and
Lithologic, faunal, seismic, and isotopic evidence from the Blake Nose (subtropical western North... more Lithologic, faunal, seismic, and isotopic evidence from the Blake Nose (subtropical western North Atlantic) links a massive release of biogenic methane ∼55.5 million years ago to a warming of deep-ocean and high-latitude surface waters, a large perturbation in the combined ocean-atmosphere carbon cycle (the largest of the past 90 million years), a mass extinction event in benthic faunas, and a radiation of mammalian orders. The deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming, massive carbon input to the global exogenic carbon cycle, pelagic carbonate dissolution, a decrease in dissolved oxygen, and a benthic foraminiferal extinction event. These events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the Blake Nose as a site of methane release.
Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstr... more Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8° ± 0.7°C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5°C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.
A high-resolution western tropical Atlantic sea surface temperature (SST) record from the Cariaco... more A high-resolution western tropical Atlantic sea surface temperature (SST) record from the Cariaco Basin on the northern Venezuelan shelf, based on Mg/Ca values in surface-dwelling planktonic foraminifera, reveals that changes in SST over the last glacial termination are synchronous, within ±30 to ±90 years, with the Greenland Ice Sheet Project 2 air temperature proxy record and atmospheric methane record. The most prominent deglacial event in the Cariaco record occurred during the Younger Dryas time interval, when SSTs dropped by 3° to 4°C. A rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature, atmospheric methane, and high-latitude changes during the Younger Dryas.
Records of planktonic and benthic foraminiferal d 18 O and planktonic Mg/Ca from core TR163-22, j... more Records of planktonic and benthic foraminiferal d 18 O and planktonic Mg/Ca from core TR163-22, just northwest of the Gala´pagos Islands, reveal a detailed (250-450 year resolution) climate history of the region over the last 135 thousand years (kyr). Sea surface temperatures (SSTs), reconstructed from G. ruber Mg/Ca, averaged 24.370.4 1C during the Holocene, 22.670.6 1C during marine isotope stage (MIS) 2, 3 and 4, and 26.070.9 1C during MIS 5e. Changes in SST lead changes in both planktonic and benthic d 18 O by an average $3 kyr, suggesting that SST changes in this region predated continental ice volume changes. Changes in SST display clear millennial scale variability, especially in marine isotope stage 3, with behavior somewhat similar to Antarctic proxy air temperature and South Pacific SST records. Removal of the temperature component from the planktonic d 18 O record demonstrates that glacialinterglacial d 18 O-water changes at this site were 1.070.2%, similar to estimates for mean ocean shifts, implying that salinity changes due to regional hydrological variation between the Last Glacial Maximum and Holocene in the Gala´pagos region were minimal. Comparison between the TR163-22 SST record and an SST record from core TR163-19 North of the Equatorial Front reveals a largely similar broadscale climate history, suggesting that changes in the Gala´pagos region were caused by large scale forcing rather than by local or regional dynamical changes. Changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large-scale climate changes in the eastern equatorial Pacific.
ABSTRACT Santa Barbara Basin (SBB) is well known for producing high quality paleoclimate reconstr... more ABSTRACT Santa Barbara Basin (SBB) is well known for producing high quality paleoclimate reconstructions, but the validity of correlations between the basin and other regions rests upon age model accuracy. Yet, the two independent and well-established chronologies based on varve counting and radiocarbon dating do not consistently agree during the last two millennia. Here the validity of age model assumptions is tested including whether 1) the regional reservoir age of surface waters was invariably 641 ± 119 years through time, and/or 2) SBB laminae couplets are consistently annual varves and counted with sufficient precision. This high-resolution 14C study of SBB sediments compares 49 mixed planktonic foraminiferal carbonate and 20 terrestrial organic carbon 14C dates to the varve chronology, to extend the high-resolution paleoclimate chronology of the basin back ∼2000 years. Evidence indicates that regional reservoir ages do not remain constant through time with ΔR, (i.e. regional reservoir age minus variations in the global mixed-layer ocean reservoir age) fluctuating between 80 and 350 years. Second, there is a consistent (R2 = 0.96) undercounting of the varves between 150 and ∼1700 AD based on a new varying ΔR 14C chronology, indicating that some laminae couplets may not be annual. Loss of varves may occur when low riverine input and infrequent winter storm activity during drought intervals fail to supply a siliciclastic layer.
The relationship between water column processes and sedimentation was investigated using a five y... more The relationship between water column processes and sedimentation was investigated using a five year time series of biweekly water column measurements and continuous sediment trap collections in the Santa Barbara Basin, California. Conditions during the strong El Niño period of 1997-98 were compared to those during the previous years and the post El Niño period. Suspended particulate concentrations of chlorophyll a (chl a), particulate organic carbon (POC), particulate organic nitrogen (PON) and biogenic silica (bSi) normally underwent a seasonal cycle characterized by high phytoplankton abundance in the spring, dominated by diatoms, followed by lower concentrations of biogenic particles throughout the rest of the year. Maxima in sinking fluxes of POC, PON, bSi and lithogenic silica (lSi) generally occurred during the summer. Prior to the El Niño period, molar ratios of C/N, Si/C and Si/N were all higher in sinking particulate material relative to particulate material suspended in the upper 75 m. Si/N and Si/C ratios were highest in the spring and summer in both surface and sinking pools. During the 1997-98 El Niño, the seasonal evolution of the density structure of surface waters was altered by the presence of a water mass high in temperature and low in salinity. The depression of the thermocline resulted in concentrations of nitrate, phosphate and silicic acid in the upper 75 m becoming lower that those measured in other years. Mean chl a and bSi concentrations integrated from the surface to 75 m were low on an annual basis, but there were no clear changes in the seasonality of suspended particle concentrations. Perhaps unexpectedly, fluxes of POC, PON and lSi at 470 m increased during the El Niño period. Lower C/N ratios and shorter turnover times suggest increases in the export ratios of POC and PON at that time. We hypothesize that the increase in lSi flux, despite the absence of elevated concentrations of lSi in the upper 75 m, resulted from the lateral advection of particles into the region from the increased riverine discharges at the margins of the basin and subsequent scavenging of the small particles by organic material. Decreases in ratios of C/N, Si/C and Si/N in sinking particles that occurred during the El Niño were sustained until the end of the time series in June 1999, and may have resulted from a shift toward a less diatom dominated pool of sinking particles.
A new centennial-scale Mg/Ca temperature record from the California margin (ODP Site 1017E) revea... more A new centennial-scale Mg/Ca temperature record from the California margin (ODP Site 1017E) reveals large millennial-scale oscillations between 10 to 60 kyr. This record indicates that sea surface temperature on the California Margin warmed rapidly on the deglacial by 7.4 AE 0.8 C, and was preceded by a pre-Bølling temperature oscillation of 2.6 AE 1.2 C. Millennial-scale events of the last glacial episode were marked by sea surface temperature oscillations of between 3 and 7 C on the California margin, and interstadials were associated with an increase in surface water salinity. The data are consistent with evidence for a glacial southward shift in the polar jet stream and concomitant strengthening of the relatively cold, fresh California Current during stadial events. The data also support previous hypotheses suggesting a tight coupling between the North Atlantic and northeast Pacific response to climate instability of the last glacial episode.
Oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate ... more Oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions, with those of benthic foraminifera providing information on the deep oceans. Reconstructions are complicated by interspecies isotopic offsets that result from microhabitat preferences (carbonate precipitation in isotopically distinct environments) and vital effects (species-specific metabolic variation in isotopic fractionation). We provide correction factors for early Cenozoic benthic foraminifera commonly used for isotopic measurements (Cibicidoides spp., Nuttallides truempyi, Oridorsalis spp., Stensioina beccariiformis, Hanzawaia ammophila, and Bulimina spp.), showing that most yield reliable isotopic proxies of environmental change. The statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies. Interspecies isotopic offsets appear to have changed through the Cenozoic, either (1) as a result of evolutionary changes or (2) as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies. Regardless of the reason, the assumption that isotopic offsets have remained constant through the Cenozoic has introduced an $1-2°C uncertainty into deep sea paleotemperature calculations. In addition, we compare multiple species isotopic data from a western North Atlantic section that includes the Paleocene-Eocene thermal maximum to determine the most reliable isotopic indicator for this event. We propose that Oridorsalis spp. was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time; it may be the best recorder at other locations and for other extreme events also.
We have developed cold-end Mg/Ca-temperature calibrations for three common Arctic benthic foramin... more We have developed cold-end Mg/Ca-temperature calibrations for three common Arctic benthic foraminifera, Islandiella norcrossi/helenae, Melonis barleeanus, and Cassidulina neoteretis, and compare the three calibrations in a late Holocene downcore record (0-4000 cal yr B.P.). The calibration and downcore trends for the three Arctic species extend the observation that Mg incorporation into benthic foraminifera is species specific. For the calibration we use a set of CTD casts, bottom water d 18 O seawater measurements, and surface grab-samples collected from the Iceland margin (cruise B997) and the Greenland margin (cruise BS1191). Water depth of sites used ranges from 165 to 656 m, while spatial bottom temperature ranges from 0 to 7°C. Mg/Ca values ranged from 1.02 to 1.47 for I. norcrossi/helenae, 0.64 to 2.21 for M. barleeanus, and 0.93 to 1.38 mmol/mol for C. neoteretis. We calibrated Mg/Ca content against isotopic calcification temperature (calculated using T = 16.9 À 4.0*(d 18 O calcite corrected for vital effect À d 18 O seawater)). Exponential calibrations for the three species are as follows: I. norcrossi/helenae Mg/Ca = 1.051 ± 0.03 * exp(0.060 ± 0.011 * T), M. barleeanus Mg/Ca = 0.658 ± 0.07 * exp(0.137 ± 0.020 * T), and C. neoteretis Mg/Ca = 0.864 ± 0.07 * exp(0.082 ± 0.020 * T). On the basis of Mg/Ca in these benthic species the downcore record from core MD99-2269 is reconstructed. Bottom temperature values are interpreted to reflect variable inflow of Atlantic and Arctic water to the north Iceland shelf during the last 4000 cal yr B.P. All three reconstructions show a decline by 0.1°C per century from circa 1500-0 cal yr B.P., which coincides with an increase in Arctic benthic foraminifera abundances and a rise in sea ice proxies in the same core. Intriguingly, C. neoteretis diverges periodically to higher average temperature (Atlantic water conditions) than shown by M. barleeanus or I. norcrossi/helenae (which both show Arctic water temperature) circa 1500-4000 cal yr B.P.
Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca a... more Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca and Sr/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg/Ca and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of ±0.2°C and ±0.5°C, respectively. The analysis of foraminifera suggests an interlaboratory variance of about ±8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about ±2-3°C. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about ±1-2°C) and a bias (about 1°C) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.
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