ALBERT

Description: Insight into past changes of upper ocean stratification, circulation, and nutrient signatures rely on our knowledge of the apparent calcification depth (ACD) and ecology of planktonic foraminifera, which serve as archives for paleoceanographic relevant geochemical signals. The ACD of different species varies strongly between ocean basins, but also regionally. We constrained foraminiferal ACDs in the western Pacific warm pool (Manihiki Plateau) by comparing stable oxygen and carbon isotopes (d18Ocalcite, d13Ccalcite) as well as Mg/Ca ratios from living planktonic foraminifera to in-situ physical and chemical water mass properties (temperature, salinity, d18Oseawater, d13CDIC). Our analyses point to Globigerinoides ruber as the shallowest dweller, followed by Globigerinoides sacculifer, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata and Globotaloides hexagonus inhabiting increasingly greater depths. These findings are consistent with other ocean basins; however, absolute ACDs differ from other studies. The uppermost mixed-layer species G. ruber and G. sacculifer denote mean calcification depths of ~95 m and ~120 m, respectively. These Western Pacific ACDs are much deeper than in most other studies and most likely relate to the thick surface mixed layer and the deep chlorophyll maximum in this region. Our results indicate that N. dutertrei appears to be influenced by mixing waters from the Pacific equatorial divergence, while P. obliquiloculata with an ACD of ~160 m is more suitable for thermocline reconstructions. ACDs of G. hexagonus reveal a deep calcification depth of ~450 m in oxygen-depleted, but nutrient-rich water masses, consistent to other studies. As the d13C of G. hexagonus is in near-equilibrium with ambient seawater, we suggest this species is suitable for tracing nutrient conditions in equatorial water masses originating in extra-topical regions.

Description: The internal development of the tropicalWest Pacific Warm Pool and its interaction with high latitude ocean regions on geological timescales is only poorly constrained. Based on two newly recovered sediment cores fromthe southeastern margin of the West Pacific Warm Pool (northern and southern Manihiki Plateau), we provide new aspects on the dynamically interacting ocean circulation at surface, subsurface, thermocline, and deep thermocline levels during the Pleistocene (~2.5-0.5 Ma). Notably, the variability of thermocline and deep thermocline(~150-400 m water depth) foraminiferal Mg/Ca-based temperatures with up to ~6 °C amplitude variations exceeds those at shallower depths (down to ~120 m) with only ~2-3 °C temperature variations. A major gradual reorganization of the West Pacific Warm Pool oceanography occurred during the transitional timeperiod of ~1.7-1.35 Ma. Prior to ~1.7 Ma, pronounced meridional and latitudinal gradients in sea-surface to subsurface ocean properties point to the eastward displacement of the West Pacific Warm Pool boundaries, with the South Pacific Convergence Zone being shifted further northeastward across Manihiki Plateau. Simultaneously, the low amplitude variations of thermocline and deep thermocline temperatures refer to an overall deep and stable thermocline. The meridional and zonal gradients in sea-surface and subsurface ocean propertieswithin the West Pacific Warm Pool reveal a pronounced change after 1.5 Ma, leading to a more southward position of the warm South Pacific Convergence Zone between ~1.35-0.9 Ma and ~0.75-0.5 Ma. Synchronous to the changes in the upper ocean, the deeper water masses experienced high amplitude variations in temperature, most prominently since ~1.5 Ma. This and the dynamically changing thermocline were most likely associated to the impact of southern- sourced mode waters, which might have developed coincidently with the emergence of the East Pacific Cold Tongue and high latitude sea-surface cooling.

Description: This data set contains results of analyses performed on core M125-34-2 (retrieved during R/V METEOR Expeditin M125 in Spring 2016) from the cold water coral-bearing Bowie Mound, located off Cabo Frio, Eastern Brazil. Analyses were performed to determine the paleoenvironmental conditions that favored or prevented coral growth. The data comprises cold water coral contents and bioturbation index based on CT-scanning, benthic foraminiferal isotopes (C and O), 13C of organic material, sortable silt, elemental ratios based on XRF core-scanning, mineral content based on Rietveld refinement of XRD data, as well as bulk TOC content and Corganic/Ntotal ratios. For comparison an off-mound site (M125-50-3) was analyzed for benthic foraminiferal isotopes (C and O) and sortable silt.