Sea surface temperature reconstruction from biomarker in sediments off Portugal

High resolution reconstructions of sea surface temperature (Uk'37-SST), coccolithophore associations and continental input (total organic carbon, higher plant n-alkanes, n-alkan-1-ols) in core D13882 from the shallow Tagus mud patch are compared to SST records from deep-sea core MD03-2699 and other western Iberian Margin cores. Results reveal millennial-scale climate variability over the last deglaciation, in particular during the LGIT. In the Iberian margin, Heinrich event 1 (H1) and the Younger Dryas (YD) represent two extreme episodes of cold sea surface condition separated by a marine warm phase that coincides with the Bølling-Allerød interval (B-A) on the neighboring continent. Following the YD event, an abrupt sea surface warming marks the beginning of the Holocene in this region. SSTs recorded in core D13882 changed, however, faster than those at deep-sea site MD03-2699 and at the other available palaeoclimate sequences from the region. While the SST values from most deep-sea cores reflect the latitudinal gradient detected in the Iberian Peninsula atmospheric temperature proxies during H1 and the B-A, the Tagus mud patch (core D13882) experienced colder SSTs during both events. This is most certainly related to a supplementary input of cold freshwater from the continent to the Tagus mud patch, a hypothesis supported by the high contents of terrigenous biomarkers and total organic carbon as well as by the dominance of tetra-unsaturated alkenone (C37:4) observed at this site. The comparison of all western Iberia SST records suggests that the SST increase that characterizes the B-A event in this region started 1000 yr before meltwater pulse 1A (mwp-1A) and reached its maximum values during or slightly after this episode of substantial sea-level rise. In contrast, during the YD/ Holocene transition, the sharp SST rise in the Tagus mud patch is synchronous with meltwater pulse IB. The decrease of continental input to the mud patch conflrms a sea level rise in the region. Thus, the synchronism between the maximum warming in the mid-latitudes off the western Iberian margin, the adjacent landmasses and Greenland indicates that mwp-lB and the associated sea-level rise probably initiated in the Northern Hemisphere rather than in the South.

Sea surface temperature variations in the western Mediterranean Sea

A high-resolution sea surface temperature (SST) reconstruction of the western Mediterranean was accomplished using two independent, algae-based molecular organic proxies, i.e. the UK'37 index based on long-chain unsaturated ketones and the novel long-chain diol index (LDI) based on the relative abundances of C28 and C30 1,13- and 1,15-diols. Two marine records, from the western and eastern Alboran Sea basin, spanning the last 14 and 20 kyr, respectively, were studied. Results from the surface sediments suggest that the two proxies presently reflect seasons with similar SST, or simply annual mean SST. Both proxy records reveal the transition from the Last Glacial Maximum to the Holocene in the eastern Alboran Sea with an SST increase of ca. 7 °C for UK'37 and 9 °C for LDI. Minimum SSTs (10-12 °C) are reached at the end of the Last Glacial Maximum and during the last Heinrich event with a subsequent rapid SST increase in LDI-SST towards the beginning of the Bölling period (20 °C), while UK'37-SST remains constantly low (~12 °C). The Bölling-Alleröd is characterized by a rapid increase and subsequent decrease in UK'37-SST, while the LDI-SST decrease continuously. Short-term fluctuations in UK'37-SST are probably related to availability of nutrients and seasonal changes. The Younger Dryas is recorded as a short cold interval followed by progressively warmer temperatures. During the Holocene, the general lower UK'37-derived temperature values in the eastern Alboran (by ca. 1.5-2 °C) suggest a southeastward cold water migration by the western Alboran gyre and divergence in the haptophyte blooming season between both basins.

Ages and stable isotope ratios from speleothem calcite from Cold Water Cave, Iowa

High-precision uranium-thorium mass spectrometric chronology and 18O-13C isotopic analysis of speleothem calcite from Cold Water Cave in northeast Iowa have been used to chart mid-Holocene climate change. Significant shifts in d18O and d13C isotopic values coincide with well-documented Holocene vegetation changes. Temperature estimates based on 18O/16O ratios suggest that the climate warmed rapidly by about 3°C at 5900 years before present and then cooled by 4°C at 3600 years before present. Initiation of a gradual increase in ?d13C at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present.

Sea surface temperature reconstruction for the LGM

The southwest Pacific Ocean covers a broad range of surface-water conditions ranging from warm, salty water in the subtropical East Australian Current to fresher, cold water in the Circumpolar Current. Using a new database of planktonic foraminifera assemblages (AUSMAT-F2), we demonstrate that the modern analog technique can be used to accurately reconstruct the magnitude of sea-surfacetemperature (SST) in this region. We apply this technique to data from 29 deep-sea cores along a meridional transect of the southwest Pacific Ocean to estimate the magnitude of SST cooling during the Last Glacial Maximum. We find minimal cooling in the tropics (0°-2°C), moderate cooling in the subtropical midlatitudes (2°-6°C), and maximum cooling to the southeast of New Zealand (6°-10°C). The magnitude of cooling at the sea surface from the tropics to the temperate latitudes is found to generally be less than cooling at the surface of adjacent land masses.

Sea surface temperature estimation for MIS 16 of IODP Site 306-U1313

Hudson Strait (HS) Heinrich Events, ice-rafting events in the North Atlantic originating from the Laurentide ice sheet (LIS), are among the most dramatic examples of millennial-scale climate variability and have a large influence on global climate. However, it is debated as to whether the occurrence of HS Heinrich Events in the (eastern) North Atlantic in the geological record depends on greater ice discharge, or simply from the longer survival of icebergs in cold waters. Using sediments from Integrated Ocean Drilling Program (IODP) Site U1313 in the North Atlantic spanning the period between 960 and 320 ka, we show that sea surface temperatures (SSTs) did not control the first occurrence of HS Heinrich(-like) Events in the sedimentary record. Using mineralogy and organic geochemistry to determine the characteristics of ice-rafting debris (IRD), we detect the first HS Heinrich(-like) Event in our record around 643 ka (Marine Isotope Stage (MIS) 16), which is similar as previously reported for Site U1308. However, the accompanying high-resolution alkenone-based SST record demonstrates that the first HS Heinrich(-like) Event did not coincide with low SSTs. Thus, the HS Heinrich(-like) Events do indicate enhanced ice discharge from the LIS at the end of the Mid-Pleistocene Transition, not simply the survivability of icebergs due to cold conditions in the North Atlantic.

Sea-surface temperature reconstruction of sediment core JT96-09PC

Changes of sea surface temperature (SST) in the subarctic NE Pacific over the last 16,000 calendar years before present (16 kyr BP) have been inferred from the study of C37 alkenone unsaturation in a sediment core from the western Canadian continental slope. Between 16.0 and 11.0 kyr, three distinct cold phases (6-7°C) interrupt two warmer periods (9-10°C). Within the 2sigma range of the radiocarbon based time control, the observed SST oscillations correspond to the Oldest Dryas, the Bolling, the Older Dryas, the Allered, and the Younger Dryas periods in the GISP2 d180 record. These results represent the first high resolution marine paleotemperature estimates off the northern West coast of North America and imply that the climate of this region may be very strongly coupled to that of the North Atlantic. Given the fast rates of SST change (1°C/40-80 yr), such coupling must be controlled by atmospheric transmission of the climate signal.

Alkenones and TEX86 temperature proxies for core-top sediments from the southern Adriatic Sea

The Mediterranean Sea is at the transition between temperate and tropical air masses and as such of importance for studying climate change. The Gulf of Taranto and adjacent SW Adriatic Sea are at the heart of this region. Their sediments are excellently suited for generating high quality environmental records for the last millennia with a sub-decadal resolution. The quality of these records is dependent on a careful calibration of the transfer functions used to translate the sedimentary lipid signals to the local environment. Here, we examine and calibrate the UK'37 and TEX86 lipid-based temperature proxies in 48 surface sediments and relate these to ambient sea surface temperatures and other environmental data. The UK'37-based temperatures in surface sediments reflect winter/spring sea surface temperatures in agreement with other studies demonstrating maximum haptophyte production during the colder season. The TEX86-based temperatures for the nearshore sites also reflect winter sea surface temperatures. However, at the most offshore sites, they correspond to summer sea surface temperatures. Additional lipid and environmental data including the distribution of the BIT index and remote-sensed chlorophyll-a suggest a shoreward increase of the impact of seasonal and spatial variability in nutrients and control of planktonic archaeal abundance by primary productivity, particle loading in surface waters and/or overprint by a cold-biased terrestrial TEX86 signal. As such the offshore TEX86 values seem to reflect a true summer signal to the effect that offshore UK'37 and TEX86 reconstruct winter and summer temperature, respectively, and hence provide information on the annual temperature amplitude.

Sea surface temperature reconstruction for Mediterranean Sea samples

Alkenone unsaturation ratios and planktonic delta18O records from sediment cores of the Alboran, Ionian and Levantine basins in the Mediterranean Sea show pronounced variations in paleo-temperatures and -salinities of surface waters over the last 16,000 years. Average sea surface temperatures (SSTs) are low during the last glacial (averages prior to 13,000 years: 11-15°C), vary rapidly at the beginning of the Holocene, and increase to 17-18°C at all sites during S1 formation (dated between 9500 and 6600 calendar years). The modern temperature gradient (2-3°C) between the Mediterranean sub-basins is maintained during formation of sapropel S1 in the Eastern Mediterranean Sea. After S1, SSTs have remained uniform in the Alboran Sea at 18°C and have fluctuated around 20°C in the Ionian and Levantine Basin sites. The delta18O of planktonic foraminifer calcite decreases by 2 per mil from the late glacial to S1 sediments in the Ionian Basin and by 2.8 per mil in the Levantine Basin. In the Alboran Sea, the decrease is 1.7 per mil. Of the 2.8 per mil decrease in the Levantine Basin, the effect of global ice volume accounts for a maximum of 1.05 per mil and the temperature increase explains only a maximum of 1.3 per mil. The remainder is attributed to salinity changes. We use the temperature and salinity estimates to calculate seawater density changes. They indicate that a reversal of water mass circulation is not a likely explanation for increased carbon burial during S1 time. Instead, it appears that intermediate and deep water formation may have shifted to the Ionian Sea approximately 2000 years before onset of S1 deposition, because surface waters were as cold, but saltier than surface water in the Levantine Basin during the Younger Dryas. Sapropel S1 began to form at the same time, when a significant density decrease also occurred in the Ionian Sea.

Sea-surface temperature reconstruction of ODP Hole 175-1078C

A prominent feature in the Southeast Atlantic is the Angola-Benguela Front (ABF), the convergence between warm tropical and cold subtropical upwelled waters. At present, the sea-surface temperature (SST) gradient across the ABF and its position are influenced by the strength of southeasterly (SE) trade winds. Here, we present a record of changes in the ABF SST gradient over the last 25 kyr. Variations in this SST contrast indicate that periods of strengthened SE trade-wind intensity occurred during the Last Glacial Maximum, the Younger Dryas, and the Mid to Late Holocene, while Heinrich Event 1, the early part of the Bølling-Allerød, and the Early Holocene were periods of weakened SE trade-winds.