The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, ... more The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, interannual, and decadal timescales is the source of climate extremes throughout the tropics and beyond. Tropical cyclones, heatwaves, flash floods, droughts, and El Niño have severe effects on ecosystems and societies globally. Projecting their amplitude and frequency changes in a warming climate requires knowledge of how the tropical ocean-atmosphere system operated in the past. Tropical shallow-water corals have great potential for extending the short and rather sparse instrumental record of sea surface observations at monthly resolution. Coral records deliver quantitative information about the fluctuations of sea surface temperature and hydrology on seasonal, interannual, and decadal timescales, with precise chronology. They provide a paleo-observational constraint on climate model simulations of past and future tropical ocean-atmosphere variability. This article highlights selected recent achievements in coral-based reconstructions of surface ocean conditions during recent centuries, the Holocene, the last deglaciation, and the last interglacial period. Future work combining ultrahigh-resolution coral reconstructions, novel analytical techniques, advanced statistical methods, and Earth system modeling will contribute to improved projections of tropical marine climate variability and the fates of coral reef ecosystems.
The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, ... more The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, interannual, and decadal timescales is the source of climate extremes throughout the tropics and beyond. Tropical cyclones, heatwaves, flash floods, droughts, and El Niño have severe effects on ecosystems and societies globally. Projecting their amplitude and frequency changes in a warming climate requires knowledge of how the tropical ocean-atmosphere system operated in the past. Tropical shallow-water corals have great potential for extending the short and rather sparse instrumental record of sea surface observations at monthly resolution. Coral records deliver quantitative information about the fluctuations of sea surface temperature and hydrology on seasonal, interannual, and decadal timescales, with precise chronology. They provide a paleo-observational constraint on climate model simulations of past and future tropical ocean-atmosphere variability. This article highlights selected recent achievements in coral-based reconstructions of surface ocean conditions during recent centuries, the Holocene, the last deglaciation, and the last interglacial period. Future work combining ultrahigh-resolution coral reconstructions, novel analytical techniques, advanced statistical methods, and Earth system modeling will contribute to improved projections of tropical marine climate variability and the fates of coral reef ecosystems.
The early last glacial termination was characterized by intense North Atlantic cooling and weak o... more The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation. This interval between ~18,000 and 14,600 years ago, known as Heinrich Stadial 1, was accompanied by a disruption of global climate and has been suggested as a key factor for the termination. However, the response of interannual climate variability in the tropical Pacific (El Niño-Southern Oscillation) to Heinrich Stadial 1 is poorly understood. Here we use Sr/Ca in a fossil Tahiti coral to reconstruct tropical South Pacific sea surface temperature around 15,000 years ago at monthly resolution. Unlike today, interannual South Pacific sea surface temperature variability at typical El Niño-Southern Oscillation periods was pronounced at Tahiti. Our results indicate that the El Niño-Southern Oscillation was active during Heinrich Stadial 1, consistent with climate model simulations of enhanced El Niño-Southern Oscillation variability at that time. Furthermore, a greater El Niño-Southern Oscillation influence in the South Pacific during Heinrich Stadial 1 is suggested, resulting from a southward expansion or shift of El Niño-Southern Oscillation sea surface temperature anomalies.
Tropical southwestern Pacific temperatures are of vital importance to the Great Barrier Reef (GBR... more Tropical southwestern Pacific temperatures are of vital importance to the Great Barrier Reef (GBR), but the role of sea surface temperatures (SSTs) in the growth of the GBR since the Last Glacial Maximum remains largely unknown. Here we present records of Sr/Ca and d 18 O for Last Glacial Maximum and deglacial corals that show a considerably steeper meridional SST gradient than the present day in the central GBR. We find a 1–2 °C larger temperature decrease between 17° and 20°S about 20,000 to 13,000 years ago. The result is best explained by the northward expansion of cooler subtropical waters due to a weakening of the South Pacific gyre and East Australian Current. Our findings indicate that the GBR experienced substantial meridional temperature change during the last deglaciation, and serve to explain anomalous deglacial drying of northeastern Australia. Overall, the GBR developed through significant SST change and may be more resilient than previously thought.
Variations in the biotic composition of marine shallow water carbonates document global climatic ... more Variations in the biotic composition of marine shallow water carbonates document global climatic changes. However, a discontinuous stratigraphic record and uncertainties regarding the ages limit the significance of shallow water carbonates as palaeoclimatic archives on geological time-scales. Notwithstanding these deficits, the environmental information stored in the skeleton of reef biota is a unique source of information that resolves seasonal to interannual climate variability in geological time. Application of the method to corals from carbonate rocks is usually restricted to the past 130,000 yr, because the aragonite skeleton undergoes rapid diagenetic alteration. Consequently, reconstructions resolving seasonal to interannual climate variability of the more distant geological time are rare. We describe exceptionally well-preserved corals ( Porites) as old as Late Miocene (10 million years) from the island of Crete (eastern Mediterranean, Greece). Stable isotope records ( δ18O, δ13C) reflect seasonal changes in sea surface temperature and symbiont autotrophy. Spectral analysis of a 67-yr coral δ18O record reveals significant variance at interannual time-scales (2-5 yr) that show similarities to Late Quaternary eastern Mediterranean climate variability. Supported by simulations with a complex atmospheric general circulation model coupled to a mixed-layer ocean model, we suggest that climate dynamics in the eastern Mediterranean may reflect atmospheric variability related to the Icelandic Low 10 million years ago.
ABSTRACT This study aimed at quantifying the amplitudes of seasonality and interannual to centenn... more ABSTRACT This study aimed at quantifying the amplitudes of seasonality and interannual to centennial climate variability in the Caribbean region throughout the Holocene, by using marine (shallow-water corals) and terrestrial (speleothems) climate archives, and climate model simulations (COSMOS). Sea-surface temperature (SST) variability on interdecadal to multidecadal timescales was more pronounced during the mid-Holocene compared to the late Holocene. The amplitude of the SST annual cycle was within the present-day range throughout most of the last 6,000 years. Exceptions include slightly increased SST seasonality at 6,200 years ago, which can be attributed mainly to insolation forcing on orbital timescales, and an increased SST seasonality at 2,350 years ago that can be attributed to internal dynamics of the climate system (El Niño-Southern Oscillation). On multidecadal and millennial timescales, precipitation variability during the Holocene was strongly linked to SST in the North Atlantic Ocean, namely the Atlantic Multidecadal Oscillation and variations in the strength of the Atlantic Meridional Overturning Circulation.
The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean cir... more The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. These perturbations are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7 ± 0.8 kyr ago, using coral Sr/Ca and d18O records. We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials.
The large-scale boreal winter climatic patterns associated with interannual variability in a cora... more The large-scale boreal winter climatic patterns associated with interannual variability in a coral oxygen isotope (d 18 O) record from the southern Red Sea covering most of the last century are investigated. From the early 1930s to the early 1960s, the winter coral d 18 O record, reflecting temperature and salinity variations in southern Red Sea surface waters, is associated with global (or large scale) sea surface temperature (SST) and 850 mb geopotential height (Z850) anomalies which project on the corresponding patterns associated with the El Niño-Southern Oscillation (ENSO). In contrast, since the early 1960s the winter coral d 18 O record is related to a Z850 pattern that reflects the ENSO-independent part of the East Asian Winter Monsoon (EAWM), which includes the Siberian High, the East Asian through, and the East Asian uppertropospheric Jet. Our results indicate a weakening of the ENSO control on interannual temperature/salinity variations in southern Red Sea surface waters in the early 1960s, due to the warming of the Indian Ocean, and suggest that information about the nonstationarity in the relationship between ENSO and two distinct modes of EAWM can be documented in southern Red Sea coral d 18 O records.
In many regions instrumental climate records are too short to resolve the full range of decadal-t... more In many regions instrumental climate records are too short to resolve the full range of decadal-to multidecadal-scale natural climate variability. Massive annually banded corals from the tropical and subtropical oceans provide a paleoclimatic archive with a seasonal resolution, documenting past variations in water temperature, hydrologic balance, and ocean circulation. Recent coral-based paleoclimatic research has focused mainly on the tropics, providing important implications on the past variability of the El Niño-Southern Oscillation (ENSO) phenomenon and decadal tropical climate variability. However, new records from some of the rare subtropical/midlatitude locations of coral growth were shown to reflect aspects of dominant modes of Northern Hemisphere climate variability, e.g. the North Atlantic Oscillation (NAO). This natural mode has important socio-economic impacts owing to its large-scale modulation of droughts, floods, storms, snowfall, and fish stocks at timescales relevant to society. Coral records extending over several centuries from key locations (e.g. northern Red Sea, Bermuda) provide the opportunity to assess recent shifts in the NAO with respect to the natural variability of the pre-instrumental period. Providing a better understanding of NAO dynamics, such paleoclimatic records, together with those derived from other paleoclimatic archives, are essential for the predictability of future European climate.
Abstract The Ras Umm Sidd coral 6180 record from the northern Red Sea is the northernmost centuri... more Abstract The Ras Umm Sidd coral 6180 record from the northern Red Sea is the northernmost centuries long coral time series that is currently available in seasonal resolution (AD 1750-1995). Here we investigate climate patterns associated with the coral 6180 time series separately for boreal winter and summer, using instrumental and reconstructed climate fields for the European-Middle East region. The winter coral 6180 record is associated with dominant modes of sea-level pressure, temperature and ...
ABSTRACT Previous studies have demonstrated the potential for the Li content of coral aragonite t... more ABSTRACT Previous studies have demonstrated the potential for the Li content of coral aragonite to record information about environmental conditions, but no detailed study of tropical corals exists. Here we present the Li and Mg to Ca ratios at a bimonthly to monthly resolution over 25 years in two modern Porites corals, the genus most often used for paleoclimate reconstructions in the tropical Indo-Pacific. A strong relationship exists between coral Li/Ca and locally measured SST, indicating that coral Li/Ca can be used to reconstruct tropical SST variations. However, Li/Ca ratios of the skeleton deposited during 1979–1980 do not track local SST well and are anomalously high in places. The Mg/Ca ratios of this interval are also anomalously high, and we suggest Li/Ca can be used to reconstruct tropical SST only when Mg/Ca data are used to carefully screen for relatively rare biological effects. Mg/Li or Li/Mg ratios provide little advantage over Li/Ca ratios, except that the slope of the Li/Mg temperature relationship is more similar between the two corals. The Mg/Li temperature relationship for the coral that experienced a large temperature range is similar to that found for cold water corals and aragonitic benthic foraminifera in previous studies. The comparison with data from other biogenic aragonites suggests the relationship between Li/Mg and water temperature can be described by a single exponential relationship. Despite this hint at an overarching control, it is clear that biological processes strongly influence coral Li/Ca, and more calibration work is required before widely applying the proxy.
Combined seasonal to monthly resolution coral skeletal y 18 O, Sr/Ca, and Mg/Ca records are repor... more Combined seasonal to monthly resolution coral skeletal y 18 O, Sr/Ca, and Mg/Ca records are reported for one modern and two late Holocene Porites lutea corals from a fringing reef at Leizhou Peninsula, the northern coast of the South China Sea (SCS). All the profiles for the period 1989-2000 reveal annual cycles well correlated with instrumental sea surface temperatures (SST), and display broad peaks in summer and narrow troughs in winter, reflecting seasonal growth rate variations. Calibration against instrumental SST yields the following equations: y 18 O=À0.174(F0.010)ÂSST(8C)À1.02(F0.27) (MSWD=5.8), Sr/ Ca (mmol/mol) =À0.0424(F0.0031)ÂSST(8C)+9.836(F0.082) (MSWD=8.6), and Mg/Ca (mmol/mol) =0.110(F0.009)ÂSST(8C)+ 1.32(F0.23) (MSWD=55). The scatter in the Mg/Ca-SST relationship is much larger than analytical uncertainties can account for, suggesting the presence of SST-unrelated components in the Mg/Ca variation.
ABSTRACT To study long-term variations in surface ocean δ13C, we investigated coral skeletal δ13C... more ABSTRACT To study long-term variations in surface ocean δ13C, we investigated coral skeletal δ13C records of 20 colonies of the shallow-water coral Porites spp. from the northern Gulf of Aqaba and the northern Red Sea. The coral colonies represent different water depths, a wide range of different periods (Last Interglacial, Holocene, the last centuries, the last decades), and various growth rates. Records from modern and fossil corals show irregular seasonal cycles, attributed mainly to the seasonal cycle of light. No attenuation in the amplitude of the seasonal skeletal δ13C cycle with depth is evident, and no significant correlation between mean annual coral δ13C and water depth was observed in the modern corals. The mean coral extension rates show no clear relationship with mean skeletal δ13C values. The average skeletal δ13C value of modern corals was − 2.74 ± 0.49‰, offset from both calcite and aragonite equilibrium values by about 5.22‰ and 6.26‰, respectively. Modern corals reveal a clear trend toward lighter skeletal δ13C values since the year 1974. At longer timescales, the skeletal δ13C values from Last Interglacial and Holocene corals and from coral records extending back to the mid- to late 18th century reveal much heavier δ13C values compared to values from 1960 to the present. The trend toward lighter skeletal δ13C values over the last decades can be attributed to changes in the δ13C of the dissolved inorganic carbon of the ambient seawater due to the addition of anthropogenically derived CO2 (13C Suess effect) to the atmosphere. Other factors such as the metabolic effects of corals may account for the modulation of skeletal δ13C on shorter timescales. A centuries-long coral record from the northern Red Sea reveals a magnitude of decrease in skeletal δ13C comparable to global trends (1960–1990), whereas a centuries-long coral record from the northern Gulf of Aqaba indicates a larger decrease over the same period, probably due to local effects. In conclusion, the combined carbon isotope records obtained from Porites spp. corals from the northern Red Sea seem to be suited to provide information on long-term world-wide changes in atmospheric CO2.
The environmental interpretation of the 13C/12C variations in the skeletons of massive corals is ... more The environmental interpretation of the 13C/12C variations in the skeletons of massive corals is still a matter of debate. A 19-year seasonal skeletal 13C/12C record of a shallow-water Porites coral from the northern Red Sea (Gulf of Aqaba) documents interannual events of extraordinarily large plankton blooms, indicated by anomalous •3C depletions in the coral skeleton. These blooms are caused by deep vertical water mass mixing, convectively driven in colder winters, which results in increased supplies of nutrients to the surface waters. The deep vertical mixings can sometimes be driven by the cooling occurring throughout the Middle East after large tropical volcanic eruptions. We therefore have evidence in our coral skeletal 13C/12C record for an indirect volcanic signal of the eruptions of E1 Chich6n (1982) and Mount Pinatubo (1991). Deep mixing induced 13C/12C variations of the dissolved inorganic carbon in the surface waters can be neglected at this location. We therefore suggest that the •3C skeletal depletions can be best explained by changes in the coral's autotrophy-heterotrophy diet, through increased heterotrophic feeding on zooplankton during the blooms. Increased feeding on •3Cdepleted zooplankton or increased heterotrophy at the expense of autotrophy can both •3 result in a C-depleted coral skeleton. However, this suggestion requires more testing. If our conclusions are substantiated, seasonal skeletal •3C/r2C records of corals which change from autotrophy under normal conditions to increased heterotrophy during bloom events may be used as indicators of ocean paleoproductivity at interannual resolution, available from no other source. 1. corals on the seasonal timescale is mainly controlled by the photosynthetic activity of the coral's endosymbiotic algae, and it is therefore attributed to the seasonal light cycle, cloudiness, or water column transparency [Fairbanks and Dodge, 1979; Piitzold, 1984; McConnaughey, 1989a; Wellington and Dunbar, ]. Endosymbiotic photosynthesis preferentially fixes 12C relative to 13C into organic carbon, thus enriching the internal dissolved inorganic carbon (DiC) "pool" from which calcification in corals takes place with 13C. In general, periods of higher photosynthesis should lead to increased concentrations of 13C in coral skeletons [Fairbanks and Dodge, 1979; Swart, 1983; McConnaughey, 1989a]. It is widely assumed that photosynthesis withdraws and respiration adds 13C-depleted carbon to the internal DIC pool [McConnaughey et al., 1997]. Variations in the 8•3C of the DIC of the seawater have also been shown to affect the coral skeletal 813C signal [Swart et al., 1996]. On the other hand, the possible importance of changes in the autotrophy-heterotrophy diet of corals for the 813C signal in their skeletons has also been pointed out [Carriquiry et al., 1994; Swart et al., 1996]. Heterotrophy means coral feeding on allochthonous sources of organic carbon, mainly zooplankton with its typical 13C-depleted isotopic signature, and a resulting contribution of 13C-depleted respiratory CO2 to the coral's internal DIC pool. This is opposite to the process where organic carbon is usually derived by photosynthetic corals, i.e., from photosynthesis of the endosymbiotic algae (autotrophy). Relative changes of the proportion of these two organic carbon food sources, with their different isotopic signatures, could influence the isotopic composition of the coral's internal DIC pool from which calcification takes place [Swart et al., 1996]. 30,731 30,732 FELIS ET AL.: PLANKTON BLOOMS RECORDED IN CORAL SKELETAL 8•3C
The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, ... more The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, interannual, and decadal timescales is the source of climate extremes throughout the tropics and beyond. Tropical cyclones, heatwaves, flash floods, droughts, and El Niño have severe effects on ecosystems and societies globally. Projecting their amplitude and frequency changes in a warming climate requires knowledge of how the tropical ocean-atmosphere system operated in the past. Tropical shallow-water corals have great potential for extending the short and rather sparse instrumental record of sea surface observations at monthly resolution. Coral records deliver quantitative information about the fluctuations of sea surface temperature and hydrology on seasonal, interannual, and decadal timescales, with precise chronology. They provide a paleo-observational constraint on climate model simulations of past and future tropical ocean-atmosphere variability. This article highlights selected recent achievements in coral-based reconstructions of surface ocean conditions during recent centuries, the Holocene, the last deglaciation, and the last interglacial period. Future work combining ultrahigh-resolution coral reconstructions, novel analytical techniques, advanced statistical methods, and Earth system modeling will contribute to improved projections of tropical marine climate variability and the fates of coral reef ecosystems.
The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, ... more The interaction of warm tropical ocean surface waters with the overlying atmosphere on seasonal, interannual, and decadal timescales is the source of climate extremes throughout the tropics and beyond. Tropical cyclones, heatwaves, flash floods, droughts, and El Niño have severe effects on ecosystems and societies globally. Projecting their amplitude and frequency changes in a warming climate requires knowledge of how the tropical ocean-atmosphere system operated in the past. Tropical shallow-water corals have great potential for extending the short and rather sparse instrumental record of sea surface observations at monthly resolution. Coral records deliver quantitative information about the fluctuations of sea surface temperature and hydrology on seasonal, interannual, and decadal timescales, with precise chronology. They provide a paleo-observational constraint on climate model simulations of past and future tropical ocean-atmosphere variability. This article highlights selected recent achievements in coral-based reconstructions of surface ocean conditions during recent centuries, the Holocene, the last deglaciation, and the last interglacial period. Future work combining ultrahigh-resolution coral reconstructions, novel analytical techniques, advanced statistical methods, and Earth system modeling will contribute to improved projections of tropical marine climate variability and the fates of coral reef ecosystems.
The early last glacial termination was characterized by intense North Atlantic cooling and weak o... more The early last glacial termination was characterized by intense North Atlantic cooling and weak overturning circulation. This interval between ~18,000 and 14,600 years ago, known as Heinrich Stadial 1, was accompanied by a disruption of global climate and has been suggested as a key factor for the termination. However, the response of interannual climate variability in the tropical Pacific (El Niño-Southern Oscillation) to Heinrich Stadial 1 is poorly understood. Here we use Sr/Ca in a fossil Tahiti coral to reconstruct tropical South Pacific sea surface temperature around 15,000 years ago at monthly resolution. Unlike today, interannual South Pacific sea surface temperature variability at typical El Niño-Southern Oscillation periods was pronounced at Tahiti. Our results indicate that the El Niño-Southern Oscillation was active during Heinrich Stadial 1, consistent with climate model simulations of enhanced El Niño-Southern Oscillation variability at that time. Furthermore, a greater El Niño-Southern Oscillation influence in the South Pacific during Heinrich Stadial 1 is suggested, resulting from a southward expansion or shift of El Niño-Southern Oscillation sea surface temperature anomalies.
Tropical southwestern Pacific temperatures are of vital importance to the Great Barrier Reef (GBR... more Tropical southwestern Pacific temperatures are of vital importance to the Great Barrier Reef (GBR), but the role of sea surface temperatures (SSTs) in the growth of the GBR since the Last Glacial Maximum remains largely unknown. Here we present records of Sr/Ca and d 18 O for Last Glacial Maximum and deglacial corals that show a considerably steeper meridional SST gradient than the present day in the central GBR. We find a 1–2 °C larger temperature decrease between 17° and 20°S about 20,000 to 13,000 years ago. The result is best explained by the northward expansion of cooler subtropical waters due to a weakening of the South Pacific gyre and East Australian Current. Our findings indicate that the GBR experienced substantial meridional temperature change during the last deglaciation, and serve to explain anomalous deglacial drying of northeastern Australia. Overall, the GBR developed through significant SST change and may be more resilient than previously thought.
Variations in the biotic composition of marine shallow water carbonates document global climatic ... more Variations in the biotic composition of marine shallow water carbonates document global climatic changes. However, a discontinuous stratigraphic record and uncertainties regarding the ages limit the significance of shallow water carbonates as palaeoclimatic archives on geological time-scales. Notwithstanding these deficits, the environmental information stored in the skeleton of reef biota is a unique source of information that resolves seasonal to interannual climate variability in geological time. Application of the method to corals from carbonate rocks is usually restricted to the past 130,000 yr, because the aragonite skeleton undergoes rapid diagenetic alteration. Consequently, reconstructions resolving seasonal to interannual climate variability of the more distant geological time are rare. We describe exceptionally well-preserved corals ( Porites) as old as Late Miocene (10 million years) from the island of Crete (eastern Mediterranean, Greece). Stable isotope records ( δ18O, δ13C) reflect seasonal changes in sea surface temperature and symbiont autotrophy. Spectral analysis of a 67-yr coral δ18O record reveals significant variance at interannual time-scales (2-5 yr) that show similarities to Late Quaternary eastern Mediterranean climate variability. Supported by simulations with a complex atmospheric general circulation model coupled to a mixed-layer ocean model, we suggest that climate dynamics in the eastern Mediterranean may reflect atmospheric variability related to the Icelandic Low 10 million years ago.
ABSTRACT This study aimed at quantifying the amplitudes of seasonality and interannual to centenn... more ABSTRACT This study aimed at quantifying the amplitudes of seasonality and interannual to centennial climate variability in the Caribbean region throughout the Holocene, by using marine (shallow-water corals) and terrestrial (speleothems) climate archives, and climate model simulations (COSMOS). Sea-surface temperature (SST) variability on interdecadal to multidecadal timescales was more pronounced during the mid-Holocene compared to the late Holocene. The amplitude of the SST annual cycle was within the present-day range throughout most of the last 6,000 years. Exceptions include slightly increased SST seasonality at 6,200 years ago, which can be attributed mainly to insolation forcing on orbital timescales, and an increased SST seasonality at 2,350 years ago that can be attributed to internal dynamics of the climate system (El Niño-Southern Oscillation). On multidecadal and millennial timescales, precipitation variability during the Holocene was strongly linked to SST in the North Atlantic Ocean, namely the Atlantic Multidecadal Oscillation and variations in the strength of the Atlantic Meridional Overturning Circulation.
The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean cir... more The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. These perturbations are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7 ± 0.8 kyr ago, using coral Sr/Ca and d18O records. We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials.
The large-scale boreal winter climatic patterns associated with interannual variability in a cora... more The large-scale boreal winter climatic patterns associated with interannual variability in a coral oxygen isotope (d 18 O) record from the southern Red Sea covering most of the last century are investigated. From the early 1930s to the early 1960s, the winter coral d 18 O record, reflecting temperature and salinity variations in southern Red Sea surface waters, is associated with global (or large scale) sea surface temperature (SST) and 850 mb geopotential height (Z850) anomalies which project on the corresponding patterns associated with the El Niño-Southern Oscillation (ENSO). In contrast, since the early 1960s the winter coral d 18 O record is related to a Z850 pattern that reflects the ENSO-independent part of the East Asian Winter Monsoon (EAWM), which includes the Siberian High, the East Asian through, and the East Asian uppertropospheric Jet. Our results indicate a weakening of the ENSO control on interannual temperature/salinity variations in southern Red Sea surface waters in the early 1960s, due to the warming of the Indian Ocean, and suggest that information about the nonstationarity in the relationship between ENSO and two distinct modes of EAWM can be documented in southern Red Sea coral d 18 O records.
In many regions instrumental climate records are too short to resolve the full range of decadal-t... more In many regions instrumental climate records are too short to resolve the full range of decadal-to multidecadal-scale natural climate variability. Massive annually banded corals from the tropical and subtropical oceans provide a paleoclimatic archive with a seasonal resolution, documenting past variations in water temperature, hydrologic balance, and ocean circulation. Recent coral-based paleoclimatic research has focused mainly on the tropics, providing important implications on the past variability of the El Niño-Southern Oscillation (ENSO) phenomenon and decadal tropical climate variability. However, new records from some of the rare subtropical/midlatitude locations of coral growth were shown to reflect aspects of dominant modes of Northern Hemisphere climate variability, e.g. the North Atlantic Oscillation (NAO). This natural mode has important socio-economic impacts owing to its large-scale modulation of droughts, floods, storms, snowfall, and fish stocks at timescales relevant to society. Coral records extending over several centuries from key locations (e.g. northern Red Sea, Bermuda) provide the opportunity to assess recent shifts in the NAO with respect to the natural variability of the pre-instrumental period. Providing a better understanding of NAO dynamics, such paleoclimatic records, together with those derived from other paleoclimatic archives, are essential for the predictability of future European climate.
Abstract The Ras Umm Sidd coral 6180 record from the northern Red Sea is the northernmost centuri... more Abstract The Ras Umm Sidd coral 6180 record from the northern Red Sea is the northernmost centuries long coral time series that is currently available in seasonal resolution (AD 1750-1995). Here we investigate climate patterns associated with the coral 6180 time series separately for boreal winter and summer, using instrumental and reconstructed climate fields for the European-Middle East region. The winter coral 6180 record is associated with dominant modes of sea-level pressure, temperature and ...
ABSTRACT Previous studies have demonstrated the potential for the Li content of coral aragonite t... more ABSTRACT Previous studies have demonstrated the potential for the Li content of coral aragonite to record information about environmental conditions, but no detailed study of tropical corals exists. Here we present the Li and Mg to Ca ratios at a bimonthly to monthly resolution over 25 years in two modern Porites corals, the genus most often used for paleoclimate reconstructions in the tropical Indo-Pacific. A strong relationship exists between coral Li/Ca and locally measured SST, indicating that coral Li/Ca can be used to reconstruct tropical SST variations. However, Li/Ca ratios of the skeleton deposited during 1979–1980 do not track local SST well and are anomalously high in places. The Mg/Ca ratios of this interval are also anomalously high, and we suggest Li/Ca can be used to reconstruct tropical SST only when Mg/Ca data are used to carefully screen for relatively rare biological effects. Mg/Li or Li/Mg ratios provide little advantage over Li/Ca ratios, except that the slope of the Li/Mg temperature relationship is more similar between the two corals. The Mg/Li temperature relationship for the coral that experienced a large temperature range is similar to that found for cold water corals and aragonitic benthic foraminifera in previous studies. The comparison with data from other biogenic aragonites suggests the relationship between Li/Mg and water temperature can be described by a single exponential relationship. Despite this hint at an overarching control, it is clear that biological processes strongly influence coral Li/Ca, and more calibration work is required before widely applying the proxy.
Combined seasonal to monthly resolution coral skeletal y 18 O, Sr/Ca, and Mg/Ca records are repor... more Combined seasonal to monthly resolution coral skeletal y 18 O, Sr/Ca, and Mg/Ca records are reported for one modern and two late Holocene Porites lutea corals from a fringing reef at Leizhou Peninsula, the northern coast of the South China Sea (SCS). All the profiles for the period 1989-2000 reveal annual cycles well correlated with instrumental sea surface temperatures (SST), and display broad peaks in summer and narrow troughs in winter, reflecting seasonal growth rate variations. Calibration against instrumental SST yields the following equations: y 18 O=À0.174(F0.010)ÂSST(8C)À1.02(F0.27) (MSWD=5.8), Sr/ Ca (mmol/mol) =À0.0424(F0.0031)ÂSST(8C)+9.836(F0.082) (MSWD=8.6), and Mg/Ca (mmol/mol) =0.110(F0.009)ÂSST(8C)+ 1.32(F0.23) (MSWD=55). The scatter in the Mg/Ca-SST relationship is much larger than analytical uncertainties can account for, suggesting the presence of SST-unrelated components in the Mg/Ca variation.
ABSTRACT To study long-term variations in surface ocean δ13C, we investigated coral skeletal δ13C... more ABSTRACT To study long-term variations in surface ocean δ13C, we investigated coral skeletal δ13C records of 20 colonies of the shallow-water coral Porites spp. from the northern Gulf of Aqaba and the northern Red Sea. The coral colonies represent different water depths, a wide range of different periods (Last Interglacial, Holocene, the last centuries, the last decades), and various growth rates. Records from modern and fossil corals show irregular seasonal cycles, attributed mainly to the seasonal cycle of light. No attenuation in the amplitude of the seasonal skeletal δ13C cycle with depth is evident, and no significant correlation between mean annual coral δ13C and water depth was observed in the modern corals. The mean coral extension rates show no clear relationship with mean skeletal δ13C values. The average skeletal δ13C value of modern corals was − 2.74 ± 0.49‰, offset from both calcite and aragonite equilibrium values by about 5.22‰ and 6.26‰, respectively. Modern corals reveal a clear trend toward lighter skeletal δ13C values since the year 1974. At longer timescales, the skeletal δ13C values from Last Interglacial and Holocene corals and from coral records extending back to the mid- to late 18th century reveal much heavier δ13C values compared to values from 1960 to the present. The trend toward lighter skeletal δ13C values over the last decades can be attributed to changes in the δ13C of the dissolved inorganic carbon of the ambient seawater due to the addition of anthropogenically derived CO2 (13C Suess effect) to the atmosphere. Other factors such as the metabolic effects of corals may account for the modulation of skeletal δ13C on shorter timescales. A centuries-long coral record from the northern Red Sea reveals a magnitude of decrease in skeletal δ13C comparable to global trends (1960–1990), whereas a centuries-long coral record from the northern Gulf of Aqaba indicates a larger decrease over the same period, probably due to local effects. In conclusion, the combined carbon isotope records obtained from Porites spp. corals from the northern Red Sea seem to be suited to provide information on long-term world-wide changes in atmospheric CO2.
The environmental interpretation of the 13C/12C variations in the skeletons of massive corals is ... more The environmental interpretation of the 13C/12C variations in the skeletons of massive corals is still a matter of debate. A 19-year seasonal skeletal 13C/12C record of a shallow-water Porites coral from the northern Red Sea (Gulf of Aqaba) documents interannual events of extraordinarily large plankton blooms, indicated by anomalous •3C depletions in the coral skeleton. These blooms are caused by deep vertical water mass mixing, convectively driven in colder winters, which results in increased supplies of nutrients to the surface waters. The deep vertical mixings can sometimes be driven by the cooling occurring throughout the Middle East after large tropical volcanic eruptions. We therefore have evidence in our coral skeletal 13C/12C record for an indirect volcanic signal of the eruptions of E1 Chich6n (1982) and Mount Pinatubo (1991). Deep mixing induced 13C/12C variations of the dissolved inorganic carbon in the surface waters can be neglected at this location. We therefore suggest that the •3C skeletal depletions can be best explained by changes in the coral's autotrophy-heterotrophy diet, through increased heterotrophic feeding on zooplankton during the blooms. Increased feeding on •3Cdepleted zooplankton or increased heterotrophy at the expense of autotrophy can both •3 result in a C-depleted coral skeleton. However, this suggestion requires more testing. If our conclusions are substantiated, seasonal skeletal •3C/r2C records of corals which change from autotrophy under normal conditions to increased heterotrophy during bloom events may be used as indicators of ocean paleoproductivity at interannual resolution, available from no other source. 1. corals on the seasonal timescale is mainly controlled by the photosynthetic activity of the coral's endosymbiotic algae, and it is therefore attributed to the seasonal light cycle, cloudiness, or water column transparency [Fairbanks and Dodge, 1979; Piitzold, 1984; McConnaughey, 1989a; Wellington and Dunbar, ]. Endosymbiotic photosynthesis preferentially fixes 12C relative to 13C into organic carbon, thus enriching the internal dissolved inorganic carbon (DiC) "pool" from which calcification in corals takes place with 13C. In general, periods of higher photosynthesis should lead to increased concentrations of 13C in coral skeletons [Fairbanks and Dodge, 1979; Swart, 1983; McConnaughey, 1989a]. It is widely assumed that photosynthesis withdraws and respiration adds 13C-depleted carbon to the internal DIC pool [McConnaughey et al., 1997]. Variations in the 8•3C of the DIC of the seawater have also been shown to affect the coral skeletal 813C signal [Swart et al., 1996]. On the other hand, the possible importance of changes in the autotrophy-heterotrophy diet of corals for the 813C signal in their skeletons has also been pointed out [Carriquiry et al., 1994; Swart et al., 1996]. Heterotrophy means coral feeding on allochthonous sources of organic carbon, mainly zooplankton with its typical 13C-depleted isotopic signature, and a resulting contribution of 13C-depleted respiratory CO2 to the coral's internal DIC pool. This is opposite to the process where organic carbon is usually derived by photosynthetic corals, i.e., from photosynthesis of the endosymbiotic algae (autotrophy). Relative changes of the proportion of these two organic carbon food sources, with their different isotopic signatures, could influence the isotopic composition of the coral's internal DIC pool from which calcification takes place [Swart et al., 1996]. 30,731 30,732 FELIS ET AL.: PLANKTON BLOOMS RECORDED IN CORAL SKELETAL 8•3C
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