Stable oxygen isotope. Mg/Ca and Temperature record of Caribbean and Pacific sediments

The final phase of the closure of the Panamanian Gateway and the intensification of Northern Hemisphere Glaciation (NHG) both occurred during the Late Pliocene. Glacial-interglacial (G-IG) variations in sea level might, therefore, have had a significant impact on the remaining connections between the East Pacific and the Caribbean. Here, we present combined foraminiferal Mg/Ca and d18O measurements from Ocean Drilling Program (ODP) Site 1241 from the East Pacific and ODP Site 999 from the Caribbean. The studied time interval covers the first three major G-IG Marine Isotope Stages (MIS 95-100, ~2.5 Ma) after the intensification of NHG. Analyses were performed on the planktonic foraminifera Neogloboquadrina dutertrei and Globigerinoides sacculifer, representing water mass properties in the thermocline and the mixed-layer, respectively. Changes in sea water temperature, relative salinity, and water column stratification strongly suggest that the Panamanian Gateway temporarily closed during glacial MIS 98 and 100, as a result of changes in ice volume equivalent to a drop in sea level of 60-90 m. Reconstructed sea surface temperatures (SST) from G. sacculifer show a glacial decrease of 2.5°C at Site 1241, but increases of up to 3°C at Site 999 during glacial MIS 98 and 100 suggesting that the Panamanian Gateway closed during these glacial periods. The Mg/Ca-temperatures of N. dutertrei remain relatively stable in the East Pacific, but do show a 3°C warming in the Caribbean at the onset of these glacial periods suggesting that the closing of the gateway also changed the water column stratification. We infer that the glacial closure of the gateway allowed the Western Atlantic Warm Pool to extend into the southern Caribbean, increasing SST (G. sacculifer) and deepening the thermocline (N. dutertrei). Additionally, ice volume appears to have become large enough during MIS 100 to survive the relatively short lasting interglacial MIS 99 so that the gateway remained closed. Towards the end of MIS 98, during MIS 97 and into MIS 96 temperatures on both sides are mostly similar suggesting water masses exchanged again. Additionally, Caribbean variations in SST and d18Owater follow a precession-like cyclicity rather than the obliquity-controlled variations characteristic of the East-Pacific and many other tropical areas, suggesting that regional atmospheric processes related to the trade winds and the Intertropical Convergence Zone (ITCZ) had a dominant impact in the Caribbean.

Geochemical data and magnetic measurements of IODP Expedition 308, Hole U1319A from the Gulf of Mexico

A 160 m mostly turbiditic late Pleistocene sediment sequence (IODP Expedition 308, Hole U1319A) from the Brazos-Trinity intraslope basin system off Texas was investigated with paleo- and rock magnetic methods. Numerous layers depleted in iron oxides and enriched by the ferrimagnetic iron-sulfide mineral greigite (Fe3S4) were detected by diagnostic magnetic properties. From the distribution of these layers, their stratigraphic context and the present geochemical zonation, we develop two conceptual reaction models of greigite formation in non-steady depositional environments. The "sulfidization model" predicts single or twin greigite layers by incomplete transformation of iron monosulfides with polysulfides around the sulfate methane transition (SMT). The "oxidation model" explains greigite formation by partial oxidation of iron monosulfides near the iron redox boundary during periods of downward shifting oxidation fronts. The stratigraphic record provides evidence that both these greigite formation processes act here at typical depths of about 12-14 mbsf and 3-4 mbsf. Numerous "fossil" greigite layers most likely preserved by rapid upward shifts of the redox zonation denote past SMT and sea floor positions characterized by stagnant hemipelagic sedimentation conditions. Six diagenetic stages from a pristine magnetite-dominated to a fully greigite-dominated magnetic mineralogy were differentiated by combination of various hysteresis and remanence parameters.

AMS 14C dating points, isotopic compositions, Mg/Ca ratios and sea surface temperatures of sediment cores GeoB10029-4 and GeoB10038-4

Quantifying the spatial and temporal sea surface temperature (SST) and salinity changes of the Indo-Pacific Warm Pool is essential to understand the role of this region in connection with abrupt climate changes particularly during the last deglaciation. In this study we reconstruct SST and seawater d18O of the tropical eastern Indian Ocean for the past 40,000 years from two sediment cores (GeoB 10029-4, 1°30'S, 100°08'E, and GeoB 10038-4, 5°56'S, 103°15'E) retrieved offshore Sumatra. Our results show that annual mean SSTs increased about 2-3 °C at 19,000 years ago and exhibited southern hemisphere-like timing and pattern during the last deglaciation. Our SST records together with other Mg/Ca-based SST reconstructions around Indonesia do not track the monsoon variation since the last glacial period, as recorded by terrestrial monsoon archives. However, the spatial SST heterogeneity might be a result of changing monsoon intensity that shifts either the annual mean SSTs or the seasonality of G. ruber towards the warmer or the cooler season at different locations. Seawater d18O reconstructions north of the equator suggest fresher surface conditions during the last glacial and track the northern high-latitude climate change during the last deglaciation. In contrast, seawater ?18O records south of the equator do not show a significant difference between the last glacial period and the Holocene, and lack Bølling-Allerød and Younger Dryas periods suggestive of additional controls on annual mean surface hydrology in this part of the Indo-Pacific Warm Pool.

(Table A1) Isotopic ratios of Sr, Nd, and Pb for sediments in ODP Leg 138 sites

The provenance of eolian dust supplied to deep-sea sediments has the potential to offer insights into changes in past atmospheric circulation. Specifically, measuring temporal changes in dust provenance can shed light on changes in the mean position of the Intertropical Convergence Zone (ITCZ), a region acting as a barrier separating wind-blown material derived from northern versus southern hemisphere sources. Here we have analyzed Nd, Sr, and Pb isotope ratios in the operationally-defined detrital component extracted from deep-sea sediments in the eastern equatorial Pacific (EEP) along a meridional transect at 110°W from 3°S to 7°N (ODP Leg 138, sites 848-853). Sr isotope results show that barite Sr has a significant influence on 87Sr/86Sr isotope ratios of samples in the upwelling zone of the EEP. However, sites located >3° or more away from the equator (sites 852 and 853) are believed to not be affected by barite Sr and provide useful detrital Sr signals. 208Pb/206Pb and 207Pb/206Pb ratios in all cores fall into the Pb-isotope space of five potential dust sources (Asia, North and Central/South America, Sahara, and Australia), with no distinct isotopic fingerprinting of the dominant source(s). epsilon-Nd values were most valuable for discerning detrital source provenance, and their values at all sites, ranging from ~5.46 to ~3.25, were more unradiogenic for sediments deposited during the last glacial than for those deposited during the Holocene. There are distinct latitudinal trends in the epsilon-Nd values, with more radiogenic values further south and less radiogenic values further north, excluding site 848. This distinction holds true for both Holocene and last glacial periods. For the most southerly site, 848, we invoke, for the first time, a distinct southern hemisphere Australian source as being responsible for the unradiogenic Nd isotope ratios. Both average last glacial and Holocene epsilon-Nd values show similar sharp gradients along the transect between 5.29°N and 2.77°N, suggesting little movement of the glacial ITCZ in the EEP. However, during the deglacial, this gradient is stronger and shifted further north between 5.29°N and 7.21°N, suggesting a more northerly, possibly stronger, deglacial ITCZ.