Description: OS51C-1004 Dissolved radiogenic Nd isotopes (εNd), rare earth element (REE), Ba, and nutrient concentrations combined with oxygen isotopes retrieved along a section between Spitsbergen and Greenland at approximately 79°N during the ARK XXVII/1 cruise in 2012 were measured to characterize the origin and mixing of the water masses in the Fram Strait. Deep waters below 500 m are nearly constant in Nd concentration (CNd) around 16 pmol/kg and εNd signatures range from -9.5±0.2 to -10.9±0.2. The heavy REE to light REE ratio (HREE/LREE) ranges from 4 to 5. Ba concentrations range from 47 to 58 nmol/kg, increasing slightly with depth. These homogeneous signatures do not allow identification of distinct deep water masses. The upper 500 m of the water column close to the Western Svalbard margin including the shelf is relatively warm and saline (T ≤ 5.5°C, S ≤ 35.1) and shares characteristics of Atlantic Water (AW) including low CNd (~15 pmol/kg) and relatively unradiogenic εNd signatures (-12.2±0.2). This water is also characterized by HREE/LREE around 4 and CBa around 50 nmol/kg. Low salinity surface waters on the East Greenland shelf have unradiogenic εNd signatures similar to AW (-12.4±0.3) but in contrast to AW high CNd of up to 37 pmol/kg. At the same time the HREE/LREE ratio is relatively low (~3.5) and CBa reaches 73 nmol/kg. This suggests a significant freshwater contribution either from the McKenzie or the Lena rivers. Eastwards of these freshwater-influenced waters (at ~5°W), admixture of a Pacific component characterized by a more radiogenic εNd (-8.8±0.2) and high nutrient concentrations outcropping at surface was detected. Waters of the same origin are present on the East Greenland shelf at about 150 m depth. Based on these data we use mass balance calculations to determine the fractions of sea ice meltwater, Eurasian run-off, North American run-off, and Arctic seawater and compare these results with our εNd and REE data.

Description: Late Pliocene changes in the advection of Mediterranean Outflow Water (MOW) derivates were reconstructed at northeast Atlantic DSDP/ODP sites 548 and 982 and compared to records of WMDW at West Mediterranean Site 978. Neodymium isotope (εNd) values more positive than −10.5/−11 reflect diluted MOW derivates that spread almost continuously into the northeast Atlantic from 3.7 to 2.55 Ma, reaching Rockall Plateau Site 982 from 3.63 to 2.75 Ma. From 3.4 to 3.3 Ma average MOW temperature and salinity increased by 2°–4 °C and ~1 psu both at proximal Site 548 and distal Site 982. The rise implies a rise in flow strength, coeval with a long-term rise in both west Mediterranean Sea surface salinity by almost 2 psu and average bottom water salinity (BWS) by ~1 psu, despite inherent uncertainties in BWS estimates. The changes were linked with major Mediterranean aridification and a drop in African monsoon humidity. In contrast to model expectations, the rise in MOW salt discharge after 3.4 Ma did not translate into improved ventilation of North Atlantic Deep Water, since it possibly was too small to significantly influence Atlantic Meridional Overturning Circulation. Right after ~2.95 Ma, with the onset of major Northern Hemisphere Glaciation, long-term average bottom water temperature (BWT) and BWS at Site 548 dropped abruptly by ~5 °C and ~1–2 psu, in contrast to more distal Site 982, where BWT and BWS continued to oscillate at estimates of ~2 °C and 1.5–2.5 psu higher than today until ~2.6 Ma. We relate the small-scale changes both to a reduced MOW flow and to enhanced dilution by warmwaters of a strengthenedNorth Atlantic Current temporarily replacingMOWderivates at Rockall Plateau.

Description: Proxy records of hydrologic variability in the West Pacific Warm Pool (WPWP) have revealed wide-scale changes in past convective activity in response to orbital and sub-orbital climate forcings. However, attributing proxy responses to regional changes in WPWP hydrology versus local variations in precipitation requires independent records linking the terrestrial and marine realms. We present high-resolution stable isotope, UK'37 sea-surface temperature, X-ray fluorescence (XRF) core scanning and coccolithophore-derived paleoproductivity records covering the past 120 ka from International Marine Global Change (IMAGES) Program Core MD06-3075 (6°29' N, 125°50' E, water depth 1878 m), situated in the Davao Gulf on the southern side of Mindanao. XRF-derived log(Fe/Ca) records provide a robust proxy for runoff-driven sedimentary discharge from Mindanao, whilst past changes in local productivity are associated with variable freshwater runoff and stratification of the surface layer. Significant precessional-scale variability in sedimentary discharge occurred during Marine Isotope Stage (MIS) 5, with peaks in discharge contemporaneous with Northern Hemisphere summer insolation minima. We attribute these changes to the latitudinal migration of the Intertropical Convergence Zone (ITCZ) over the WPWP together with variability in the strength of the Walker circulation acting on precessional timescales. Between 60 and 15 ka sedimentary discharge at Mindanao was muted, displaying little orbital- or millennial-scale variability, likely in response to weakened precessional insolation forcing and lower sea level driving increased subsidence of air masses over the exposed Sunda Shelf. These results highlight the high degree of local variability in the precipitation response to past climate changes in the WPWP.