Age determination of sediments of Site LO09-14 (Table 1)

A composite record (LO09-14) of three sediment cores from the subpolar North Atlantic (Reykjanes Ridge) was investigated in order to assess surface ocean variability during the last 11 kyr. The core site is today partly under the influence of the Irminger Current (IC), a branch of the North Atlantic Drift continuing northwestward around Iceland. However, it is also proximal to the Sub-Arctic Front (SAF) that may cause extra dynamic hydrographic conditions. We used statistical methods applied to the fossil assemblages of diatoms to reconstruct quantitative sea surface temperatures (SSTs). Our investigations give evidence for different regional signatures of Holocene surface oceanographic changes in the North Atlantic. Core LO09-14 reveal relatively low and highly variable SSTs during the early Holocene, indicating a weak IC and increased advection of subpolar water over the site. A mid-Holocene thermal optimum with a strong IC occurs from 7.5 to 5 kyr and is followed by cooler and more stable late Holocene surface conditions. Several intervals throughout the Holocene are dominated by the diatom species Rhizosolenia borealis, which we suggest indicates proximity to a strongly defined convergence front, most likely the SAF. Several coolings, reflecting southeastward advection of cold and ice-bearing waters, occur at 10.4, 9.8, 8.3, 7.9, 6.4, 4.7, 4.3 and 2.8 kyr. The cooling events recorded in the LO09-14 SSTs correlate well with both other surface records from the area and the NADW reductions observed at ODP Site 980 indicating a surface-deepwater linkage through the Holocene.

(Table 1) Age determination of ODP Sites 124-769 and 124-768

The Sulu Sea is located in the 'warm pool' of the western Pacific Ocean, where mean annual temperatures are the highest of anywhere on Earth. Because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat, understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change. Changes in the oxygen isotope composition of planktonic foraminifera from Sulu Sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial-interglacial and millenial timeseales, and such records have been obtained for the late Pleistocene epoch and the last deglaciation (Linsley and Thunell, 1990, doi:10.1029/PA005i006p01025; Lindley and Dunbar, 1994, doi:10.1029/93PA03216; Kudrass et al., 1991, doi:10.1038/349406a0). Here I present results that extend the millenial time resolution record back to 150,000 years before present. On timescales of around 10,000 years, the Sulu Sea oxygen-isotope record matches changes in sea level deduced from coral terraces on the Huon peninsula (Chappell and Shackleton, doi:10.1038/324137a0). This is particularly the case during isotope stage 3 (an interglacial period 23,000 to 58,000 years ago) where the Sulu Sea oxygen-isotope record deviates from the SPECMAP deep-ocean oxygen-isotope record (Imbrie et al., 1984). Thus these results support the idea (Chappell and Shackleton, doi:10.1038/324137a0; Shackleton, 1987, doi:10.1016/0277-3791(87)90003-5) that there were higher sea levels and less continental ice during stage 3 than the SPECMAP record implies and that sea level during this interglacial was just 40-50 metres below present levels. The subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought.

(Table 1) Age determination of sediment core MD02-2589

Sortable silt mean grain sizes together with oxygen and carbon isotopic data produced on the benthic foraminiferal species Fontbotia wuellerstorfi are used to construct high-resolution records of near-bottom flow vigour and deep water ventilation at a core site MD02-2589 located at 2660 m water depth on the southern Agulhas Plateau. The results suggest that during glacial periods (marine oxygen isotope stages 2 and 6, MIS 2 and MIS 6, respectively), there was a persistent contribution of a well-ventilated water mass within the Atlantic to Indian oceanic gateway with a d13C signature similar to present-day Northern Component Water (NCW), e.g., North Atlantic Deep Water (NADW). The records of chemical ventilation and near-bottom flow vigor reflect changes in the advection of northern source waters and meridional variability in the location of the Antarctic Circumpolar Current and its associated fronts. We suggest that during Termination II (TII), changes in chemical ventilation are largely decoupled from near-bottom physical flow speeds. A mid-TII climate optimum is associated with a low-flow speed plateau concurrent with a period of increased ventilation shown in the benthic d13C of other Southern Ocean records but not in our benthic d13C of MD02-2589. The climate optimum is followed by a period of southern cooling around 128 ka coincident with a stronger influence of NCW to interglacial levels at around 124 ka. All proxy records show a near synchronous and rapid shift during the transition from MIS 5a-4 (73 ka). This large event is attributed to a rapid decrease in NADW influence and replacement over the Agulhas Plateau by southern source waters.

Age determination and stable isotope record of sediment core MR06-04_PC23A

Millennial-scale variability in the behavior of North Pacific Intermediate Water during the last glacial and deglacial period, and its association with Dansgaard-Oeschger (D-O) cycles and Heinrich events, are examined based on benthic foraminiferal oxygen and carbon isotopes (d18Obf and d13Cbf) and %CaCO3 using a sediment core recovered from the northeastern slope of the Bering Sea. A suite of positive d18Obf excursions at intermediate depths of the Bering Sea, which seem at least in part associated with increases in the d18Obf gradients between the Bering and Okhotsk Seas, suggest the Bering Sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period. Absence of such d18Obf gradients during periods of high surface productivity in the Bering and Okhotsk Seas, which we correlate to D-O interstadials, suggests a reduction in intermediate water production in the Bering Sea and subsequent introduction of nutrient-rich deep waters from the North Pacific into intermediate depths of the Bering Sea. We argue that a reorganization of atmospheric circulation in the high-latitude North Pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern Bering Sea. The resulting salinity increase in the cold surface waters could have initiated intermediate (and deep) water formation that spread out to the North Pacific.