Sea surafce temperature reconstruction for sediment core SU81-18

Reconstructing the impact of Heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events. A high-resolution study of a marine sediment core from the Iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low-salinity arctic water masses during the last three Heinrich events. These paleoclimatic time series reveal the internal complexity of each of the last three Heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments.

Holocene sea-surface reconstructions for the Californian margin

Time series of alkenone unsaturation indices gathered along the California margin reveal large (4° to 8°C) glacial-interglacial changes in sea surface temperature (SST) over the past 550,000 years. Interglacial times with SSTs equal to or exceeding that of the Holocene contain peak abundances in the pollen of redwood, the distinctive component of the temperate rainforest of the northwest coast of California. In the region now dominated by the California Current, SSTs warmed 10,000 to 15,000 years in advance of deglaciation at each of the past five glacial maxima. SSTs did not rise in advance of deglaciation south of the modern California Current front. Glacial warming along the California margin therefore is a regional signal of the weakening of the California Current during times when large ice sheets reorganized wind systems over the North Pacific. Both the timing and magnitude of the SST estimates suggest that the Devils Hole (Nevada) calcite record represents regional but not global paleotemperatures, and hence does not pose a fundamental challenge to the orbital ("Milankovitch") theory of the Ice Ages.

Reconstruction of sea-surface conditions at middle to high latitudes of the Northern Hemisphere

A new calibration database of census counts of organic-walled dinoflagellate cyst (dinocyst) assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the Northern Hemisphere after standardisation of taxonomy and laboratory procedures. The database comprises 940 reference data points from the North Atlantic, Arctic and North Pacific oceans and their adjacent seas, including the Mediterranean Sea, as well as epicontinental environments such as the Estuary and Gulf of St. Lawrence, the Bering Sea and the Hudson Bay. The relative abundance of taxa was analysed to describe the distribution of assemblages. The best analogue technique was used for the reconstruction of Last Glacial Maximum (LGM) sea-surface temperature and salinity during summer and winter, in addition to sea-ice cover extent, at sites from the North Atlantic (n=63), Mediterranean Sea (n=1) and eastern North Pacific (n=1). Three of the North Atlantic cores, from the continental margin of eastern Canada, revealed a barren LGM interval, probably because of quasi-permanent sea ice. Six other cores from the Greenland and Norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation. At the remaining sites (n= 54), relatively close modern analogues were found for most LGM samples, which allowed reconstructions. The new LGM results are consistent with previous reconstructions based on dinocyst data, which show much cooler conditions than at present along the continental margins of Canada and Europe, but sharp gradients of increasing temperature offshore. The results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea-ice cover, whereas relatively warm conditions may have prevailed offshore in summer. From these data, we hypothesise low thermal inertia in a shallow and low-density surface water layer.

Palynology and dinoflagellate counts of surface sediments, and sea surface conditions, of sites in the North Pacific

Palynological analyses were performed on 53 surface sediment samples from the North Pacific Ocean, including the Bering and Okhotsk Seas (37-64°N, 144°E-148°W), in order to document the relationships between the dinocyst distribution and sea-surface conditions (temperatures, salinities, primary productivity and sea-ice cover). Samples are characterized by concentrations ranging from 18 to 143816 cysts/cm**3 and the occurrence of 32 species. A canonical correspondence analysis (CCA) was carried out to determine the relationship between environmental variables and the distribution of dinocyst taxa. The first and second axes represent, respectively, 47% and 17.8% of the canonical variance. Axis 1 is positively correlated with all parameters except to the sea-ice and primary productivity in August, which are on the negative side. Results indicate that the composition of dinocyst assemblages is mostly controlled by temperature and that all environmental variables are correlated together. The CCA distinguishes 3 groups of dinocysts: the heterotrophic taxa, the genera Impagidinium and Spiniferites as well as the cyst of Pentapharsodinium dalei and Operculodinium centrocarpum. Five assemblage zones can be distinguished: 1) the Okhotsk Sea zone, which is associated to temperate and eutrophic conditions, seasonal upwellings and Amur River discharges. It is characterized by the dominance of O. centrocarpum, Brigantedinium spp. and Islandinium minutum; 2) the Western Subarctic Gyre zone with subpolar and mesotrophic conditions due to the Kamchatka Current and Alaska Stream inflows. Assemblages are dominated by Nematosphaeropsis labyrinthus, Pyxidinopsis reticulata and Brigantedinium spp.; 3) the Bering Sea zone, depicting a subpolar environment, influenced by seasonal upwellings and inputs from the Anadyr and Yukon Rivers. It is characterized by the dominance of I. minutum and Brigantedinium spp.; 4) the Alaska Gyre zone with temperate conditions and nutrient-enriched surface waters, which is dominated by N. labyrinthus and Brigantedinium spp. and 5) the Kuroshio Extension-North Pacific-Subarctic Current zone characterized by a subtropical and oligotrophic environment, which is dominated by O. centrocarpum, N. labyrinthus and warm taxa of the genus Impagidinium. Transfer functions were tested using the modern analog technique (MAT) on the North Pacific Ocean (= 359 sites) and the entire Northern Hemisphere databases ( = 1419 sites). Results confirm that the updated Northern Hemisphere database is suitable for further paleoenvironmental reconstructions, and the best results are obtained for temperatures with an accuracy of +/-1.7 °C.

Sea surface reconstruction of sediment cores off West Spitsbergen

Two sediment cores from the West Spitsbergen area, Euro-Arctic margin, MD99-2304 and MD99-2305, have been investigated for paleoceanographic proxies, including benthic and planktonic foraminifera, benthic foraminiferal stable isotopes and ice rafted debris. Core MD99-2304 is located on the upper continental margin, reflecting variations in the influx of Atlantic Water in the West Spitsbergen Current. Core MD99-2305 is located in Van Mijenfjord, picturing variations in tidewater glacier activity as well as fjord-ocean circulation changes. Surface water warmer than today, was present on the margin as soon as the Van Mijenfjord was deglaciated by 11,200 cal. years BP. Relatively warm water invaded the fjord bottom almost immediately after the deglaciation. A relatively warm early Holocene was followed by an abrupt cooling at 8800 cal. years BP on the continental margin. Another cooling in the fjord record, 8000-4000 cal. years BP, is documented by an increase in ice rafted debris and an increase in benthic foraminiferal delta18O. The IRD-record indicates that central Spitsbergen never was completely deglaciated during the Holocene. Relatively cool and stable conditions similar to the present were established about 4000 cal. years BP.

Age models and sea-surface paleotemperature reconstruction of sediment cores from the eastern equatorial Atlantic

Based on the faunal record of planktonic foraminifers in three long gravity sediment cores from the eastern equatorial Atlantic, the sea-surface temperature history ove the last 750,000 years was studied at a resolution of 3,000 to 10,000 years. Detailed oxygen-isotope and paleomagnetic stratigraphy helped to identify the following major faunal events: Globorotaloides hexagonus and Globorotalia tumida flexuosa became extinct in the eastern tropical Atlantic at the isotope stage 4/5 boundary, now dated at 68,000 years B.P. The persistent occurrence of the pink variety of Globigerinoides ruber started during the late stage 12 at 410,000 years B.P. CARTUNE-age. This datum may provide an easily detectible faunal stratigraphic marker for the mid-Brunhes Chron. The updated scheme of the Ericson zones helped the recognition of a hiatus at the northwestern slope of the Sierra Leone Basin covering oxygen-isotope stages 10 to 12. Classifying the planktonic foraminifer counts into six faunal assemblages, according to the factor analysis derived model of Pflaumann (1985), the tropical and the tropical-upwelling communities account for 57 % at Site 16415, and 86 % at Site 13519, respectively of the variance of the faunal record. A largely continuous paleotemperature record for both winter and summer seasons was obtained from the top of the Sierra Leone Rise with the winter temperatures ranging between 20 and 25 °C, and the summer ones between 24 and 30 °C. The record of cores from greater water depths is frequently interrupted by samples with no-analogue faunal communities and/or poor preservation. Based on the seasonality signal, during cold periods the termal equator shifted to a geographically mnore asymmetrical northern position. Dissolution altering the faunal communities becomes stronger with greater water depth, the estimated mean minimum loss of specimens increases from 70 % to 80 % between 2,860 and 3,850 water depth although some species will be more susceptible than others. Enhanced dissolution occured during stage 4 but also during cold phases in the warm stage 7 and 9. Correlations between the Foraminiferal Dissolution Index and the estimated sea-surface temperatures are significant. Foraminiferal flux rates, negatively correlated to the flux rates of organic carbon and of diatoms, may be a result of enhanced dissolution during cold stages, destroying still more of the faunal signal than indicated by the calculated minimum loss. The fluctuations of the oxygen-isotope curves and the hibernal sea-surfave temperatures are fairly coherent. During warm oxygen-isotope stages the temperature maxima lag often by 5 to 15 ka behind the respective sotope minima. During cold stages, sea-surface temperature changes are partly out of phase and contain additional fluctuations.

Alkenone-derived UK'37 data and sea surface temperatures (SST) of sediment cores from the Gulf of Taranto (Italy)

Auxiliary data include one file with alkenone-derived UK'37 data and sea surface temperatures (SST). On these data Figs. 7 and 8 of the manuscript are based. The SST are derived from UK'37 by using the transfer function: SST = 29.876 UK'37 - 1.334 of Conte et al. (2006). The data are against the ages (in A.D.) of samples derived from cores GT91-1 (39[deg]59'23"N, 17[deg]45'25"E), GT89-3 and GT90-3 (both 39[deg]45'43"N, 17[deg]53'55"E ). Also included are composite records for UK'37 and SST. For creating the composite records, GT-89-3 was taken as reference core. In the overlapping period the GT89-3 data seem in general lower than the GT91-1 data. To accommodate for this in the composite record, the average difference (0.0343 UK'37 units; equivalent to 1.023 [deg]C) was subtracted from the GT91-1 record. Hereafter, for each depth in the overlapping interval the respective values (UK'37 or SST) of GT89-3 and GT91-1 were averaged. We have also averaged with 16 additional alkenone measurements, from 1793 to 1851, performed in the GT90-3 core.

AMS 14C dating points, isotopic compositions, Mg/Ca ratios and sea surface temperatures of sediment cores GeoB10029-4 and GeoB10038-4

Quantifying the spatial and temporal sea surface temperature (SST) and salinity changes of the Indo-Pacific Warm Pool is essential to understand the role of this region in connection with abrupt climate changes particularly during the last deglaciation. In this study we reconstruct SST and seawater d18O of the tropical eastern Indian Ocean for the past 40,000 years from two sediment cores (GeoB 10029-4, 1°30'S, 100°08'E, and GeoB 10038-4, 5°56'S, 103°15'E) retrieved offshore Sumatra. Our results show that annual mean SSTs increased about 2-3 °C at 19,000 years ago and exhibited southern hemisphere-like timing and pattern during the last deglaciation. Our SST records together with other Mg/Ca-based SST reconstructions around Indonesia do not track the monsoon variation since the last glacial period, as recorded by terrestrial monsoon archives. However, the spatial SST heterogeneity might be a result of changing monsoon intensity that shifts either the annual mean SSTs or the seasonality of G. ruber towards the warmer or the cooler season at different locations. Seawater d18O reconstructions north of the equator suggest fresher surface conditions during the last glacial and track the northern high-latitude climate change during the last deglaciation. In contrast, seawater ?18O records south of the equator do not show a significant difference between the last glacial period and the Holocene, and lack Bølling-Allerød and Younger Dryas periods suggestive of additional controls on annual mean surface hydrology in this part of the Indo-Pacific Warm Pool.

Stable isotopes, Mg/Ca ratios and sea surface temperatures on foraminifera from sediment cores off equatorial Peru during the last ~17kyr

The complex deglacial to Holocene oceanographic development in the Gulf of Guayaquil (Eastern Equatorial Pacific) is reconstructed for sea surface and subsurface ocean levels from (isotope) geochemical proxies based on marine sediment cores. At sea surface, southern sourced Cold Coastal Water and tropical Equatorial Surface Water/Tropical Surface Water are intimately related. In particular since ~10 ka, independent sea surface temperature proxies capturing different seasons emphasize the growing seasonal contrast in the Gulf of Guayaquil, which is in contrast to ocean areas further offshore. Cold Coastal Water became rapidly present in the Gulf of Guayaquil during the austral winter season in line with the strengthening of the Southeast Trades, while coastal upwelling off Peru gradually intensified and expanded northward in response to a seasonally changing atmospheric circulation pattern affecting the core locations intensively since 4 ka BP. Equatorial Surface Water, instead, was displaced and Tropical Surface Water moved northward together with the Equatorial Front. At subsurface, the presence of Equatorial Under Current-sourced Equatorial Subsurface Water was continuously growing, prominently since ~10-8 ka B.P. During Heinrich Stadial 1 and large parts of the Bølling/Allerød, and similarly during short Holocene time intervals at ~5.1-4 ka B.P. and ~1.5-0.5 ka B.P., the admixture of Equatorial Subsurface Water was reduced in response to both short-term weakening of Equatorial Under Current strength from the northwest and emplacement by tropical Equatorial Surface Water, considerably warming the uppermost ocean layers.

Strontium measurements and sea surface temperatures of corals from Xisha Island, South China Sea

A Porites coral collected from Xisha Island, South China Sea, represents a skeleton secreted in the period from 1906 to 1994. The Sr contents of the coral vary linearly with the instrument-measured sea-surface temperature (SST), giving a Sr thermometer: SST = -1.9658 x Sr + 193.26. The reconstructed SST data show that the late 20th century was warmer (about 1°C) than the early 20th century and that two cooling (1915/1916 and 1947/1948) and three warming (1935/1936, 1960/1961, and 1976/1977) shifts occurred in the century. The temperature shifts are more pronounced for winters, implying a close effect of the west Pacific warm pool and Asian monsoon and suggesting that the former is a primary force controlling the climatic system of the region. Results of this study and previously published data indicate a close link of temperature shifts between the boreal summer and the austral winter or the boreal winter and the austral summer. The annual SST anomalies in the South China Sea and the South Pacific reveal the existence of harmonic but opposite SST variations between the two regions. On the decadal scale the comparative annual SST anomalies for the South China Sea and for the equatorial west Pacific show a similarity in temperature variations, implying that the South China Sea climate is coherent with climatic regime of the tropical west Pacific.