Papers by Geert-Jan A. Brummer
Anthropogenic activities, in particular rising CO2 emissions, provoke ocean warming and acidifica... more Anthropogenic activities, in particular rising CO2 emissions, provoke ocean warming and acidification1,2, altering plankton habitats and threatening calcifying species3,4 such as planktonic Foraminifera (PF). Whether they can cope with these unprecedented rates of environmental change, through lateral migrations and vertical displacements, is unresolved. Here we show, using over a century of data from the FORCIS5 global census counts, that PF display evident poleward migratory behaviours, increasing their diversity at mid to high latitudes, and for some symbiont-barren species descending in the water column. Global PF abundance decreased by 24.24±0.11% over the last decades. Beyond lateral migrations6, our study uncovers intricate vertical migration patterns among PF species, presenting a nuanced understanding of their adaptive strategies. In projected temperature and carbonate saturation states for 2050 and 2100, low-latitude PF species will face physico-chemical environments that ...
EGU General Assembly Conference Abstracts, Apr 1, 2015
EGU General Assembly Conference Abstracts, Apr 1, 2015
AGUFM, Dec 1, 2008
We present an almost three year long record of planktonic foraminifera fluxes, oxygen and carbon ... more We present an almost three year long record of planktonic foraminifera fluxes, oxygen and carbon isotopes of Turburotalita quinqueloba and Neogloboquadrina pachyderma s. from moored sediment traps and surface plankton samples from the central Irminger Sea. The mooring area is characterised by a large annual sea surface temperature cycle, whereas temperatures at depth remain almost constant, resulting in a highly stratified upper water column during summer and virtually no stratification during winter as is evident from daily salinity and temperature measurements at approximately 200 m water depth, satellite derived sea surface temperature and occasional sea surface temperature and salinity measurements. Since salinity variability both at depth and at the surface is very small, the site is ideally suited to study the effects of thermal stratification on the fluxes and stable isotopic composition of T. quinqueloba and N. pachyderma s. The flux of N. pachyderma s. peaks twice a year (in spring and autumn), a typical productivity pattern for the sub-arctic setting. Both growing seasons account for >95% of the total annual flux and contribute about equally to the total flux. The shell flux of T. quinqueloba however, shows only a single broad peak (September), more resembling flux patterns of the arctic domain. The delta18O N. pachyderma s. from surface plankton is practically identical to the expected value; at the site N. pachyderma s. thus seems to calcify in equilibrium with seawater. Its apparent export calcification depth varies during the season: ~50 m during the spring bloom, but closer to the surface during the autumn bloom period; in both cases shallower than often reported. The average delta18O N. pachydermas. in the Irminger Sea thus reflects sea water temperature between 0 and 50 m depth. The delta18O of T. quinqueloba in plankton pump samples shows slightly lighter values than expected from inorganic calcite precipitates, but isotope values of trap samples are extremely heavy (too cold) indicating a positive offset from equilibrium values. This offset is of opposite sign than all previous studies and may question the species' suggested paleoceanographic potential. In any case the Deltadelta18O N. pachyderma s.- T. quinqueloba does not reveal any thermal stratification of the upper ocean as has been proposed for the Nordic Seas. The delta13C and flux of N. pachyderma s. show a good correlation (r2 = 0.65), probably reflecting a shared governing factor for both parameters, i.e. productivity. The flux and delta13C of T. quinqueloba seem to be independent (r2 = 0.16), which might be related to the activity of symbionts in this taxon.
EGU General Assembly Conference Abstracts, Apr 1, 2017
We report here the results of a multi-proxy study to reconstruct surface water pCO 2 concentratio... more We report here the results of a multi-proxy study to reconstruct surface water pCO 2 concentrations in the northern Arabian Sea. Our results show that δ 11 B and Mg/Ca measurements of the planktonic foraminifer Globigerinoides sacculifer yield consistent pCO 2 values with those reconstructed from the δ 13 C of alkenones when used in 1 conjunction with foraminifera δ 13 C and Cd/Ca values. They reveal that this area of the oceans has been a constant source of CO 2 to the atmosphere during the interval 5-29 ka, and that the intensity of this source was greatest between 11-17 ka, when atmospheric CO 2 levels were rising rapidly. We interpret our data as reflecting variation in the strength of the Asian summer monsoon (ASM), thus indicating that the strength of the ASM varied in phase with summer insolation over the Tibetan plateau between 5-29 ka. In contrast to a previous study (Clemens and Prell, 2003), we observe no significant lag between the rise in insolation and the response of the ASM. Rather, our data support a recent study by Rohling et al. (2009) that northern hemisphere climatic forcing factors play a greater role in controlling the intensity of the ASM during times of intense monsoon activity, and that the southern hemisphere forcing is more important during times of weak monsoons.
EGU General Assembly Conference Abstracts, Apr 1, 2018
ABSTRACT Amplitude of seasonal and inter-annual changes in seawater temperature and salinity is o... more ABSTRACT Amplitude of seasonal and inter-annual changes in seawater temperature and salinity is one of the major characteristics of the coupled ocean-atmosphere system. Reconstructing these crucial oceanographic parameters is a high priority but remains mostly unachieved. The primary obstruction in reconstructing seasonality is the presence of large and mostly unquantified biological effect on proxies for seawater temperature and salinity, such as Mg/Ca and δ18O compositions of foraminiferal shells. In this work we employed Secondary Iron Microprobe spectrometry (SIMs) to characterise variability in Mg/Ca compositions of planktonic foraminifera G. sacculifer from samples representing modern (sediment trap) and fossil (box-core) species assemblages. The sediment trap samples were collected offshore Somalia at bi-weekly intervals for one year, covering the whole seasonal cycle. To decouple seawater temperature signal from vital effect, two sediment trap samples, corresponding to the minimal and maximal sea water temperatures at the collection site, were analysed with SIMs. We also analysed G. sacculifer from core-top sample collected directly below the sediment trap site to compare between Mg/Ca variability in modern and fossil G. sacculifer populations. This information is used to investigate how accurate Mg/Ca variability is preserved in the sedimentary record and the processes that can potentially bias the signal. Based on the results of this work, we will discuss the potential for developing a quantitative proxy for past ocean seasonality as well as the methodology for generating paleoseasonality record.
The subtropical Mozambique Channel in the SW Indian Ocean displays a pronounced annual sea surfac... more The subtropical Mozambique Channel in the SW Indian Ocean displays a pronounced annual sea surface temperature (SST) cycle ranging from 25 °C to 30 °C. This annual cycle is also revealed in the remote sensing parameters surface-mixed-layer depth (SML depth), chlorophyll a, and in surface water nutrient concentrations. Superimposed on this annual cycle we find a ~70 day current cycle
Scientific Data
Planktonic Foraminifera are unique paleo-environmental indicators through their excellent fossil ... more Planktonic Foraminifera are unique paleo-environmental indicators through their excellent fossil record in ocean sediments. Their distribution and diversity are affected by different environmental factors including anthropogenically forced ocean and climate change. Until now, historical changes in their distribution have not been fully assessed at the global scale. Here we present the FORCIS (Foraminifera Response to Climatic Stress) database on foraminiferal species diversity and distribution in the global ocean from 1910 until 2018 including published and unpublished data. The FORCIS database includes data collected using plankton tows, continuous plankton recorder, sediment traps and plankton pump, and contains ~22,000, ~157,000, ~9,000, ~400 subsamples, respectively (one single plankton aliquot collected within a depth range, time interval, size fraction range, at a single location) from each category. Our database provides a perspective of the distribution patterns of planktoni...
Paleoceanography, 2010
We present an almost 3 year long time series of shell fluxes and oxygen isotopes of left-coiling ... more We present an almost 3 year long time series of shell fluxes and oxygen isotopes of left-coiling Neogloboquadrina pachyderma and Turborotalita quinqueloba from sediment traps moored in the deep central Irminger Sea. We determined their response to the seasonal change from a deeply mixed water column with occasional deep convection in winter to a thermally stratified water column with a surface mixed layer (SML) of around 50 m in summer. Both species display very low fluxes during winter with a remnant summer population holding out until replaced by a vital population that seeds the subsequent blooms. This annual population overturning is marked by a 0.7‰ increase in d 18 O in both species. The shell flux of N. pachyderma peaks during the spring bloom and in late summer, when stratification is close to its minimum and maximum, respectively. Both export periods contribute about equally and account for >95% of the total annual flux. Shell fluxes of T. quinqueloba show only a single broad pulse in summer, thus following the seasonal stratification cycle. The d 18 O of N. pachyderma reflects temperatures just below the base of the seasonal SML without offset from isotopic equilibrium. The d 18 O pattern of T. quinqueloba shows a nearly identical amplitude and correlates highly with the d 18 O of N. pachyderma. Therefore T. quinqueloba also reflects temperature near the base of the SML but with a positive offset from isotopic equilibrium. These offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species. In the Irminger Sea the species consistently show a contrast in their flux timings. Their flux-weighted Dd 18 O will thus dominantly be determined by seasonal temperature differences at the base of the SML rather than by differences in their depth habitat. Consequently, their sedimentary Dd 18 O may be used to infer the seasonal contrast in temperature at the base of the SML.
Climate of the Past, 2013
Pacific Ocean sea surface temperatures (SST) influence rainfall variability on multidecadal and i... more Pacific Ocean sea surface temperatures (SST) influence rainfall variability on multidecadal and interdecadal timescales in concert with the Pacific Decadal Oscillation (PDO) and Interdecadal Pacific Oscillation (IPO). Rainfall variations in locations such as Australia and North America are therefore linked to phase changes in the PDO. Furthermore, studies have suggested teleconnections exist between the western Indian Ocean and Pacific Decadal Variability (PDV), similar to those observed on interannual timescales related to the El Niño Southern Oscillation (ENSO). However, as instrumental records of rainfall are too short and sparse to confidently assess multidecadal climatic teleconnections, here we present four coral climate archives from Madagascar spanning up to the past 300 yr (1708-2008) to assess such decadal variability. Using spectral luminescence scanning to reconstruct past changes in river runoff, we identify significant multidecadal and interdecadal frequencies in the coral records, which before 1900 are coherent with Asian-based PDO reconstructions. This multidecadal relationship with the Asian-based PDO reconstructions points to an unidentified teleconnection mechanism that affects Madagascar rainfall/runoff, most likely triggered by multidecadal changes in North Pacific SST, influencing the Asian Monsoon circulation. In the 20th century we decouple human deforestation effects from rainfallinduced soil erosion by pairing luminescence with coral geochemistry. Positive PDO phases are associated with increased Indian Ocean temperatures and runoff/rainfall in eastern Madagascar, while precipitation in southern Africa and eastern Australia declines. Consequently, the negative PDO phase that started in 1998 may contribute to reduced rainfall over eastern Madagascar and increased precipitation in southern Africa and eastern Australia. We conclude that multidecadal rainfall variability in Madagascar and the western Indian Ocean needs to be taken into account when considering water resource management under a future warming climate.
Earth and Planetary Science Letters, 2005
The global expression of millennial-scale climatic change and the persistence of this signal in H... more The global expression of millennial-scale climatic change and the persistence of this signal in Holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations. We suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of CH 4 and N 2 O, providing a tropical mechanism of amplifying and perpetuating millennial-scale climatic changes. A multi-proxy reconstruction of the intensity of the Arabian Sea Summer Monsoon shows strong millennial-scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the Intertropical Convergence Zone and an eastward shift in the equatorial convergence zone. This reconstruction, which is based on new data from a Somali margin sediment core, is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases CH 4 and N 2 O.
Journal of Plankton Research, 2019
Diurnal vertical migration (DVM) is a widespread phenomenon in the upper ocean, but it remains un... more Diurnal vertical migration (DVM) is a widespread phenomenon in the upper ocean, but it remains unclear to what degree it also involves passively transported micro-and meso-zooplankton. These organisms are difficult to monitor by in situ sensing and observations from discrete samples are often inconclusive. Prime examples of such ambiguity are planktonic foraminifera, where contradictory evidence for DVM continues to cast doubt on the stability of species vertical habitats, which introduces uncertainties in geochemical proxy interpretation. To provide a robust answer, we carried out highly replicated randomized sampling with 41 vertically resolved plankton net hauls taken within 26 hours in a confined area of 400 km 2 in the tropical North Atlantic, where DVM in larger plankton occurs. Manual enumeration of planktonic foraminifera cell density consistently reveals the highest total cell concentrations in the surface mixed layer (top 50 m) and analysis of cell density in seven individual species representing different shell sizes, life strategies and presumed depth habitats reveals consistent vertical habitats not changing over the 26
Climate of the Past Discussions, 2019
Changeover from a glacial to an interglacial climate is considered as transitional between two st... more Changeover from a glacial to an interglacial climate is considered as transitional between two stable modes. Palaeoceanographic reconstructions using the polar foraminifera Neogloboquadrina pachyderma highlight the retreat of 15 the polar front during the last deglaciation in terms of both its decreasing abundance and stable oxygen isotope values (δ 18 O) in sediment cores. While conventional isotope analysis of pooled N. pachyderma shells show a warming trend concurrent with the retreating ice, new single shell measurements reveal that this trend is composed of two isotopically different populations that are morphologically indistinguishable. Using modern time-series as analogues for interpreting down-core data, glacial productivity in the mid North Atlantic appears limited to a single maximum in late summer, 20 followed by the melting of drifting icebergs and winter sea ice. Despite collapsing ice sheets and global warming during the deglaciation a second 'warm' population of N. pachyderma appears in a bimodal seasonal succession separated by the subpolar G. bulloides. This represents a shift in the timing of the main plankton bloom from late to early summer in a deglacial intermediate mode that persisted for ca. 10,000 years until the last deglaciation ended. When seawater temperatures exceeded the threshold values, first the "cold" (glacial) then the "warm" (deglacial) population of N. 25 pachyderma disappeared, whilst G. bulloides with a greater tolerance to higher temperatures persisted throughout the Holocene to the present day in the mid-latitude North Atlantic. Single specimen δ 18 O of polar N. pachyderma reveal a steeper rate of ocean warming during the last deglaciation than appears from conventional pooled δ 18 O average values.
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Papers by Geert-Jan A. Brummer