ALBERT

Description: The only low latitude pathway of heat and salt from the Pacific Ocean to the Indian Ocean, known as Indonesian Throughflow (ITF), has been suggested to modulate Global Mean Surface Temperature (GMST) warming through redistribution of surface Pacific Ocean heat. ITF observations are only available since ~1990s, and thus, its multidecadal variability on longer time scales has remained elusive. Here we present a 200 year bimonthly record of geochemical parameters (d18O-Sr/Ca) measured on Cocos (Keeling) corals tracking sea surface temperature (SST; Sr/Ca) and sea surface salinity (SSS; seawater-d18O-d18Osw) in the southeastern tropical Indian Ocean (SETIO). Our results show that SETIO SSS and d18Osw were impacted by ITF transport over the past 60 years, and therefore, reconstructions of Cocos d18Osw hold information on past ITF variability on longer time spans. Over the past 200 years ITF leakage into SETIO is dominated by the interannual climate modes of the Pacific Ocean (El Niño-Southern Oscillation) and Indian Ocean (Indian Ocean Dipole). Pacific decadal climate variability (represented by the Pacific Decadal Oscillation) significantly impacted ITF strength over the past 200 years determining the spatiotemporal SST and SSS advection into the Indian Ocean on multidecadal time scales. A comparison of our SETIO d18Osw record to GMST shows that ITF transport varied in synchrony with global warming rate, being predominantly high/low during GMST warming slowdown/acceleration, respectively. This hints toward an important role for the ITF in global warming rate modulation.

Description: We compare geochemical and pollen data of several well-dated, high-resolution cores to provide an integral Holocene overview of Nile outflow, sedimentation, and vegetation in and around the Nile delta. We show that the focus point of the Nile plume varied considerably, as indicated by planktonic foraminifer Globigerinoides ruber oxygen isotopes tracing Nile discharge differences in an east-west delta transect. At 13-11.5 cal kyr BP, Nile discharge was low and runoff was predominantly directed to the western part of the delta. Sediment arriving in the delta during that period was dominated by Ethiopian Highland (~Blue Nile) material, shown by high Ti/Al values of the bulk sediment, indicating dry conditions in the source area of the Blue Nile. Nile discharge increased from ~11.5 cal kyr BP, and was high across the whole delta from ~10-6.5 cal kyr BP. During this time, the Ti/Al values decreased within most Nile-delta sediments, suggesting that the relative contribution of Blue-Nile sediment decreased. This was likely due to an increased vegetation cover causing diminished erosion in the Ethiopian Highlands. Nile discharge gradually decreased from ~6.5 cal kyr BP to present. This decrease was more abrupt in the Western Province of the delta and became more gradual towards the east as the shrinking Nile runoff was directed there. The gradual decrease in precipitation in the Nile catchment area seems not to be matched by a gradual response in vegetation growing around the river plain in the lower Nile catchment. Our findings suggest a nonlinear response of northeast African vegetation to precipitation from the middle to late Holocene.

Description: This data file includes all XRF data from sapropel S5 used in the manuscript and the age per sample based on the initial age model. Each of the tabs contains the measurements at a specific resolution (of the same depth interval). The measurements were performed on core 64PE-406-E1. For all analyses, the element/totalCPS (base 10) log ratio is used. If more then 1 data point exists at a given depth, the first is used (using the "unique" command in matlab).

Description: We present high-resolution records for oxygen isotopes of the planktic foraminifer Globigerinoides ruber (d18Oruber) and bulk sediment inorganic geochemistry for Holocene-age sediments from the southeast Mediterranean. Our d18Oruber record appears to be dominated by Nile discharge rather than basin-scale salinity/temperature changes. Nile discharge was enhanced in the early to middle Holocene relative to today. The timing of the long-term maximum in Nile discharge during the early Holocene corresponds to the timing of maximum intensity of the Indian Ocean-influenced Southwest Indian summer monsoon (SIM). This coincidence suggests a major influence of an Indian Ocean moisture source on Nile discharge in the early to middle Holocene, while, presently, the Atlantic Ocean is the main moisture source. Nile discharge was highly variable on multicentennial time scale during the early to middle Holocene, being strongly influenced by variable solar activity. This solar-driven variability is also recorded in contemporaneous SIM records, however, not observed in an Atlantic Ocean-derived West African summer monsoon record from the Holocene. This supports the hypothesis that the Indian Ocean moisture source predominantly controlled Nile discharge at that time. Solar-driven variability in Nile discharge also influenced paleoenvironmental conditions in the eastern Mediterranean. Bulk sediment Ba/Al and V/Al, used as indicators for (export) productivity and redox conditions, respectively, varied both in response to solar forcing on multicentennial time scales. We suggest that changes in Nile discharge on these time scales have been concordant with nutrient inputs to, and shallow ventilation of, the eastern Mediterranean.