Description: Benthic foraminiferal assemblages and the carbon isotope composition of the epifaunal benthic foraminifera Epistominella exigua and Fontbotia wuellerstorfi have been investigated along core MD02-2589 located at the southern Agulhas Plateau (41°26.03'S, 25°15.30'E, 2660 m water depth). This study aims to evaluate changes in the benthic paleoenvironment and its influence on benthic d13C with a notable focus on E. exigua, a species associated with phytodetritus deposits and poorly studied in isotope paleoceanographic reconstructions. The benthic foraminiferal assemblages (〉63 µm) show large fluctuations in species composition suggesting significant changes in the pattern of ocean surface productivity conceivably related to migrations of the Subtropical Convergence (STC) and Subantarctic Front (SAF). Low to moderate seasonality and relatively higher food supply to the seafloor are indicated during glacial marine isotope stages (MIS) 6, 4, and 2 and during MIS 3, probably associated with the northward migration of the SAF and confluence with the more stationary STC above the southern flank of the Agulhas Plateau. The lowest organic carbon supply to the seafloor is indicated from late MIS 5b to MIS 4 as a consequence of increased influence of the Agulhas Front (AF) and/or weakening of the influence of the STC over the region. Episodic delivery of fresh organic matter, similar to modern conditions at the core location, is indicated during MIS 5c-MIS 5e and at Termination I. Comparison of this paleoenvironmental information with the paired d13C records of E. exigua and F. wuellerstorfi suggests that organic carbon offsets d13C of E. exigua from ambient bottom water d13CDIC, while its d13C amplitude, on glacial-interglacial timescales, does not seem affected by changes of organic carbon supply to the seafloor. This suggests that this species calcifies preferentially during the short time span of the year when productivity peaks and phytodetritus is delivered to the seafloor. Therefore E. exigua, while offset from d13CDIC, potentially more faithfully records the amplitude of ambient bottom water d13CDIC changes than F. wuellerstorfi, notably in settings such as the Southern Ocean that experienced substantial changes through time in the organic carbon supply to the seafloor.

Description: Evidence from paleoclimatic archives suggests that Earth's climate experienced rapid temperature changes associated with pronounced interhemispheric asymmetry during the last glacial period. Explanations for these climate excursions have converged on nonlinear interactions between ice sheets and the ocean's thermohaline circulation, but the driving mechanism remains to be identified. Here we use multidecadal marine records of faunal, oxygen isotope, and sediment proxies from the northeast Atlantic proximal to the western margins of the last glacial British Ice Sheet (BIS) to document the coupling between ice sheet dynamics, ocean circulation, and insolation changes. The core data reveal successions of short-lived (80-100 years), high-amplitude ice-rafted debris (IRD) events that were initiated up to 2000 years before the deposition of detrital carbonate during Heinrich events (HE) 1 and 2. Progressive disintegration of the BIS 19-16 kyr before present (B.P.) occurred in response to abrupt ocean-climate warmings that impinged on the northeast Atlantic during the early deglaciation. Peak IRD deposition recurs at 180-220 year intervals plausibly involving repeated breakup of glacial tidewater margins and fringing marine ice shelves. The early deglaciation culminated in a major meltwater pulse at ~16.3 kyr B.P. followed by another discharge associated with HE1 some 300 years after. We conclude that temperature changes related to external forcing and marine heat transport caused a rapid response of the BIS and possibly other margins of the Eurasian Ice Sheet. Massive but short-lived meltwater surges influenced the Atlantic meridional overturning circulation thereby contributing to North Atlantic climate variability and bipolar climatic asymmetry.

Description: [1] Planktonic d18O and Mg/Ca-derived sea surface temperature (SST) records from the Agulhas Corridor off South Africa display a progressive increase of SST during glacial periods of the last three climatic cycles. The SST increases of up to 4°C coincide with increased abundance of subtropical planktonic foraminiferal marker species which indicates a progressive warming due to an increased influence of subtropical waters at the core sites. Mg/Ca-derived SST maximizes during glacial maxima and glacial Terminations to values about 2.5°C above full-interglacial SST. The paired planktonic d18O and Mg/Ca-derived SST records yield glacial seawater d18O anomalies of up to 0.8 per mill, indicating measurably higher surface salinities during these periods. The SST pattern along our record is markedly different from a UK'37-derived SST record at a nearby core location in the Agulhas Corridor that displays SST maxima only during glacial Terminations. Possible explanations are lateral alkenone advection by the vigorous regional ocean currents or the development of SST contrasts during glacials in association with seasonal changes of Agulhas water transports and lateral shifts of the Agulhas retroflection. The different SST reconstructions derived from UK'37 and Mg/Ca pose a significant challenge to the interpretation of the proxy records and demonstrate that the reconstruction of the Agulhas Current and interocean salt leakage is not as straightforward as previously suggested.

Description: The Portuguese margin is well-suited for studies of the contrasts in North Atlantic circulation during glacial and interglacial times because of its rapid sediment accumulation rate. This paper reports a (230Thexcess)0-based study of sediment accumulation over the past 140 ky, a period which includes the last two glacial/interglacial transitions, in two cores at 2.4 and 3.5 km water depth on a slope transect at 40°N. Although the independently-determined mean sediment accumulation fluxes over the past 140 ky are unequivocally high with means of 13.2 and 10.5 g cm**-2 ky**-1 in the two cores, conventional application of the (230Thexcess)0 method yields consistently lower fluxes with means of 3.5 and 3.8 g cm**-2 ky**-1. These (230Thexcess)0 estimates are interpreted as representations of the regional depositional flux through time. This (230Thexcess)0 regional flux is composed of a carbonate flux of 〈1 g cm**-2 ky**-1and a larger and variable clay input which indicates the importance of the sea level control on the clay input to the basin. Clay flux dominates the regional sediment accumulation which has a total flux of ~2 g cm**-2 ky**-1and a CaCO3 content up to 50% in interglacial times, and a total flux up to ~5 g cm**-2 ky**-1and a CaCO3 content down to 10% in glacial times. This pattern of change of sediment composition through time is also typical of the NE Atlantic, and sediment focusing (contourite formation) appears responsible for the high actual fluxes observed in glacial compared with interglacial times on the Iberian margin. The inventories of (230Thexcess)0 exceed those which could have been supplied from the overlying water column alone over 140 ky by factors of *3.2 and *4.0 in the two cores. This is ascribed to preferential current focusing of fine sedimentary material in glacial times as a result of a systematic change in deep ocean circulation in response to climatic forcing. The presence of Heinrich events in the sediments is clearly evident, but at this southerly latitude they produce muted regional increases in accumulation flux (〈2 g cm**-2 ky**-1), apart from the large Heinrich event 4 which introduced an additional 10-20 g cm cm**-2 ky**-1 over ambient background levels.

Description: Bivalve shells from the CRP-l drillhole, Cape Roberts (Victoria Land Basin), have been analysed for their stable isotope composition to obtain information on Antarctic coastal palaeoceanography during the middle Pleistocene and early Miocene. Shells from a middle Pleistocene carbonate-rich unit (lithostratigraphic Unit 3.1; 33.82-3 1.89 metres below sea floor) have d180 values between +3.64 and +4.56 per mil PDB and d13C between +0.85 and + 1.09 per mil PDB. Oxygen isotopic compositions are close to or at equilibrium conditions with scawater at a temperature in the range of c. -2 to 0°C in the absence of melt water influx. Thus, the CRP-1 carbonate-unit was deposited under 'interglacial' polar conditions, comparable to those of the present-day and isotope stage 3 in the Ross Sea. 'Chlamys' sp. 1, retrieved from a lower Miocene diamictite at 62.19 mbsf, is the only unaltered shell of this age in CRP-1 and yielded a d18O value of -4.64 per mil PDB and d13C of -3.35 per mil PDB. These values show that palaeoceanographic conditions during early Miocene time were significantly different from those of today. The depleted stable oxygen isotope composition of the Miocene shell reflects both an appreciable input of melt or fresh water and warmer-than-present seawater temperatures.