Carles Pelejero

East Asian monsoon climate during the Late Pleistocene: high-resolution sediment records from the south China Sea

Abstract Based on the study of 10 sediment cores and 40 core-top samples from the South China Sea (SCS) we obtained proxy records of past changes in East Asian monsoon climate on millennial to bidecadal time scales over the last 220,000 years. Climate proxies such as global sea level, estimates of paleotemperature, salinity, and nutrients in surface water, ventilation of deep water, paleowind strength, freshwater lids, fluvial and/or eolian sediment supply, and sediment winnowing on the sea floor were derived from planktonic and benthic stable-isotope records, the distribution of siliciclastic grain sizes, planktonic foraminifera species, and the UK37 biomarker index. Four cores were AMS-14C-dated. Two different regimes of monsoon circulation dominated the SCS over the last two glacial cycles, being linked to the minima and maxima of Northern Hemisphere solar insolation. (1) Glacial stages led to a stable estuarine circulation and a strong O2-minimum layer via a closure of the Borneo sea strait. Strong northeast monsoon and cool surface water occurred during winter, in part fed by an inflow from the north tip of Luzon. In contrast, summer temperatures were as high as during interglacials, hence the seasonality was strong. Low wetness in subtropical South China was opposed to large river input from the emerged Sunda shelf, serving as glacial refuge for tropical forest. (2) Interglacials were marked by a strong inflow of warm water via the Borneo sea strait, intense upwelling southeast of Vietnam and continental wetness in China during summer, weaker northeast monsoon and high sea-surface temperatures during winter, i.e. low seasonality. On top of the long-term variations we found millennial- to centennial-scale cold and dry, warm and humid spells during the Holocene, glacial Terminations I and II, and Stage 3. The spells were coeval with published variations in the Indian monsoon and probably, with the cold Heinrich and warm Dansgaard–Oeschger events recorded in Greenland ice cores, thus suggesting global climatic teleconnections. Holocene oscillations in the runoff from South China centered around periodicities of 775 years, ascribed to subharmonics of the 1500-year cycle in oceanic thermohaline circulation. 102/84-year cycles are tentatively assigned to the Gleissberg period of solar activity. Phase relationships among various monsoon proxies near the onset of Termination IA suggest that summer-monsoon rains and fluvial runoff from South China had already intensified right after the last glacial maximum (LGM) insolation minimum, coeval with the start of Antarctic ice melt, prior to the δ18O signals of global sea-level rise. Vice versa, the strength of winter-monsoon winds decreased in short centennial steps only 3000–4000 years later, along with the melt of glacial ice sheets in the Northern Hemisphere.

Dansgaard‐Oeschger and Heinrich event imprints in Alboran Sea paleotemperatures

Past sea surface temperature (SST) evolution in the Alboran Sea (western Mediterranean) during the last 50,000 years has been inferred from the study of C37 alkenones in International Marine Global Change Studies MD952043 core. This record has a time resolution of ∼200 years allowing the study of millennial-scale and even shorter climatic changes. The observed SST curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period. Comparison of this Alboran record with δ18O from Greenland ice (Greenland Ice Sheet Project 2 core) shows a strong parallelism between these SST oscillations and the Dansgaard-Oeschger events. Five prominent cooling episodes standing out in the SST profile are accompanied by an anomalous high abundance of Neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals. These features and the isotopic record reflect drastic changes in the surface hydrography of the Alboran Sea in association with Heinrich events Hl–5.

High‐resolution UK 37 temperature reconstructions in the South China Sea over the past 220 kyr

Past sea surface temperatures (SST) in the northern and southern areas of the South China Sea have been reconstructed for the past 220 kyr using the UK37 alkenone index. The SST profiles follow the glacial/interglacial pattern exhibiting differences between Last Glacial Maximum and Holocene that are 1°–3°C larger than those observed at the same latitudes in the Atlantic and Pacific Oceans. In Termination I both planktonic foraminiferal δ18O and SST exhibit well-defined Bolling-Allerod and Younger Dryas events with temperature differences between both periods of 0.8° and 0.4°C in north and south, respectively. SSTs record a constant north-south difference of 1°C in the interglacials and nearly 2.5°C in the glacial stages. These differences define two distinct climatic and water circulation patterns that correspond with glacial/interglacial sea level oscillations which opened and closed water exchange with the tropical Indo-Pacific Ocean through the present Sunda Shelf.

Identification and removal of Mn‐Mg‐rich contaminant phases on foraminiferal tests: Implications for Mg/Ca past temperature reconstructions

[1] The geochemical composition of foraminifera shells from an Ocean Drilling Program site in the Panama Basin has been analyzed by several analytical techniques (LA-ICP-MS, ICP-MS, XRD, SEM, EDX) in order to identify and evaluate the occurrence of contaminant phases which may bias paleoenvironmental reconstructions. LA-ICP-MS results on uncleaned tests indicate the presence of MnMg-rich contaminant phases at the inner surfaces of the foraminiferal shells (which have Mn/Ca ratios up to 400 mmol mol 1 and Mg/Ca ratios up to 50 mmol mol 1 ). We have rigorously assessed the ability of different cleaning protocols to remove these contaminant phases and have obtained satisfactory results only when a reductive step is included. The analysis of cleaning residuals collected after each of the different cleaning steps applied reveals that high Mn values are associated with at least two different contaminant phases, of which only one is linked to high Mg values. XRD analysis further reveals that the Mn-Mg-rich phase is the Ca-Mn-Mg carbonate kutnahorite (Ca(Mn, Mg)(CO3)2). Our results demonstrate that the presence of kutnahorite-like minerals can bias Mg/Ca ratios toward higher values (by 7–36%) and lead to significant overestimation of past seawater temperatures (by 0.9 up to 6.2� C, in the case of these Panama Basin samples). Components: 11,867 words, 13 figures, 3 tables.

Paleo-perspectives on ocean acidification

The anthropogenic rise in atmospheric CO(2) is driving fundamental and unprecedented changes in the chemistry of the oceans. This has led to changes in the physiology of a wide variety of marine organisms and, consequently, the ecology of the ocean. This review explores recent advances in our understanding of ocean acidification with a particular emphasis on past changes to ocean chemistry and what they can tell us about present and future changes. We argue that ocean conditions are already more extreme than those experienced by marine organisms and ecosystems for millions of years, emphasising the urgent need to adopt policies that drastically reduce CO(2) emissions.

The correlation between the 37k index and sea surface temperatures in the warm boundary: The South China Sea

Abstract The South China Sea, due to its location and high sedimentary C 37 alkenone concentrations, is an ideal environment for the evaluation of the linear relationship between the alkenone-derived U 37 k index and sea surface temperatures (SST) at the warm boundary. The alkenone compounds in this system have been analyzed in a series of coretop sediments covering most of the areas situated far from the influence of riverine inputs. The resulting U 37 k indices have been correlated with averaged SST of various depth levels and seasons. Curve fitting of these parameters have shown that the linear U 37 k /SST relationship is maintained at the warm end, which strongly contrasts with the lack of correlation at low SST reported in other studies. The best curve fittings of the U 37 k measurements are obtained for the annually averaged 0–30 m water column temperatures, providing a linear equation, U 37 k = 0.031 T + 0.092, that is the same within error limits as those previously obtained in open ocean sites or Emiliania huxleyi cultures.

Clean-up procedures for the unbiased estimation of C37 alkenone sea surface temperatures and terrigenous n-alkane inputs in paleoceanography

Abstract Sample preparation procedure for the quick determination of C25C33 n-alkanes and the U37k index in small sediment sample amounts (ca. 1 g dry weight) have been developed. Alkaline hydrolysis and silica column fractionation are the two clean-up steps considered. The former eliminates the interferences from the sedimentary wax esters which dominate the lipid composition in high latitude Atlantic Ocean sediments. The latter has been designed to collect both lipid groups (C25C33 n-alkanes and C37 alkenones) in one single fraction avoiding the interferences from highly polar compounds which affect, in particular, the quantitative determination of the n-alkanes. The whole procedure has been shown not to affect the U37k measurements, even at low C37 ketone concentrations such as 10 ng which is the minimum threshold of total C37 alkenones in the gas chromatographic system for avoidance of adsorption-related interferences [1]. As shown with real case examples the usefulness of these clean up methods is highly dependent on the amounts of interfering lipid compounds present in the sediment extracts and their application may not be necessary for the open sea sediments present in most low latitude areas.

Holocene variations in Asian monsoon moisture: A bidecadal sediment record from the South China Sea

The East Asian monsoon system involves extensive transport of sensible/latent heat between land and sea and from low to high latitudes. Our high resolution, bidecadal marine records present a first detailed history of monsoon climate change over the Holocene. The high-amplitude perturbation in monsoon moisture centered at 8,150 years ago and the monsoon maximum in the Early Holocene show inter-hemispheric teleconnections to both a cool episode in Greenland and to the Indian monsoon monitored in the Arabian Sea. Periodicities of 84, 102 and, especially, near 775 years in monsoon variation suggest a climatic forcing both by long-term oscillations in thermohaline circulation and (possibly) solar activity cycles.

Antarctic deglacial pattern in a 30 kyr record of sea surface temperature offshore South Australia

[1] Comparison of ice cores from Greenland and Antarctica shows an asynchronous two-step warming at these high latitudes during the Last Termination. However, the question whether this asynchrony extends to lower latitudes is unclear mainly due to the scarcity of paleorecords from the Southern Hemisphere. New data from a marine core collected off South Australia (� 36S) allows a detailed reconstruction of sea-surface temperatures over the Last Termination. This confirms the existence of an Antarctic-type deglacial pattern and shows no indication of cooling associated with the Northern Hemisphere YD event. The SST record also provides a new comparison with the more extensive paleoclimatic data available from continental Australia. This shows a strong climatic link between onshore and offshore records for Australia and to Southern Hemisphere paleorecords. We also show a progressive SST drop over the last � 6.5 kyr not seen before for the Australian region. Citation: Calvo, E., C. Pelejero, P. De Deckker, and G. A. Logan (2007), Antarctic deglacial pattern in a 30 kyr record of sea surface temperature offshore South Australia, Geophys. Res. Lett., 34, L13707, doi:10.1029/2007GL029937.

Synchroneity of meltwater pulse 1a and the Bolling warming:New evidence from the South China Sea

A twofold decrease in long-chain n -alcane ( n -nonacosane) concentrations in a downcore record from the northern South China Sea indicates a rapid drop in the supply of terrigenous organic matter to the open South China Sea during the last deglaciation, paralleled by an equally rapid increase in sea-surface temperatures, corresponding with the Bolling warming at 14.7 ka. The sudden drop in terrigenous organic matter delivery to this marginal basin is interpreted to reflect a short-term response of local rivers to rapid sea-level rise, strongly implying that the Bolling warming and the onset of meltwater pulse (MWP) 1a are synchronous. This phase relation contrasts with the widely cited onset of this MWP 1a ca. 14 ka, and implies that previous studies postulating a weakening of deep-water formation in the North Atlantic due to massive meltwater discharge during MWP 1a need to be reevaluated.