(Appendix) Relative abundance of planktonic foraminifera in ODP Site 138-846 late Quaternary sediments

High-resolution records of d18O and relative abundances of planktonic foraminifers were generated for ODP Leg 138 Site 846 for the past 800 k.y., with an average sampling interval of 3.6 k.y. The time scale was constructed by correlating the benthic d18O record to the SPECMAP and ODP Site 677 d18O time scales using the mapping function technique of Martinson et al. (1981). Our observations show that variations in the foraminiferal assemblages, although influenced by dissolution, are interpretable in terms of changing characteristics of upper ocean waters. Carbonate dissolution as indicated by fragmentation of planktonic foraminifers shows concentrated variance that is coherent with d18O at the 100 and 41 k.y. orbital periods. At these periods, maximum dissolution occurs during interglacial extremes. This finding differs from previous studies that have indicated that in this region percent carbonate minimum lags global ice volume minimum. N. dutertrei and dextral N. pachyderma dominate the assemblages, but do not show consistent relationships relative to glacial-interglacial cycles. However, less abundant species G. ruber, G. menardii, G. glutinata and G. sacculifer show positive and G. bulloides negative correlation with the d18O record. Q-mode factor analysis of the Site 846 assemblages and comparison with modern assemblages suggest the following. Prior to and during interglacials, the area was considerably warmer and more subtropical than at present; during glacials, the area was colder than at present with greater upwelling and advection off the eastern boundary, and possibly a stronger Peru Current; the equatorial ôcool tongueö was also possibly stronger.

Figure 2. Downcore variations of total diatom concentration in core MD02-2529

The modern eastern equatorial Pacific (EEP) is a major natural source for atmospheric carbon dioxide and is thought to be connected to high-latitude ocean dynamics by oceanic teleconnections on glacial-interglacial timescales. A wealth of sedimentary records aiming at reconstructing last Quaternary changes in primary productivity and nutrient utilization have been devoted to understanding those linkages between the EEP and other distant oceanic areas. Most of these records are, however, clustered in the pelagic EEP cold tongue, with comparatively little attention devoted to coastal areas. Here we present downcore measurements of the composition and concentration of the diatom assemblage together with opal (biogenic silica) concentration at site MD02-2529 recovered in the coastal Panama Basin. Piston core MD02-2529, collected in an area affected by a multitude of processes, provides evidence for strong variations in diatom production at the millennial timescale during the last glacial cycle. The maxima in total diatom concentration occurred during the early marine isotopic stage (MIS) 4 as well as during the MIS 4/3 transition and MIS 3. Rapid changes in diatom concentrations during the MIS 3 mimics Bond cycles as independently recorded by the SSS estimation derived from planktonic foraminifera from the same core. Such patterns indicate a clear linkage between diatom production in the coastal EEP and rapid climate changes in the high-latitude North Atlantic. In parallel, the long-term succession of the diatom community from coastal diatoms, predominantly thriving during MIS 5 and 4, towards pelagic diatoms, dominant during MIS 3 and 2, points to a long-term change in the surface hydrology. During Heinrich Events, diatoms strongly reduced their production, probably due to enhanced stratification in the upper water column. After the last glacial maximum, diatom production and valve preservation strongly decreased in response to the advection of nutrient (H2SiO4)-depleted, warmer water masses. Our high-resolution record highlights how regional climatic processes can modulate rapid changes in siliceous primary production as triggered by wind-induced local upwelling, indicating that millennial climatic variability can overtake other prominent hydrological processes such as those related to silicic acid leakage.

(Table 1) Annual melt rates of the South Branch of Jacobshavn Isbrae between July 1984-1985

Photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of Jakobshavn Isbrae, west Greenland. The thickness of the floating tongue determined from hydrostatic equilibrium tapers from ~940 m near the grounding zone to ~600 m near the terminus. Feature tracking on orthophotos shows speeds on the July 1985 ice tongue to be nearly constant (~18.5 m/d), indicating negligible dynamic thinning. The thinning of the ice tongue is mostly due to submarine melting with average rates of 228 ± 49 m/yr (0.62 ± 0.13 m/d) between the summers of 1984 and 1985. The cause of the high melt rate is the circulation of warm seawater (thermal forcing of up to 4.2°C) beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone. We believe that this buoyancy-driven convection is responsible for a deep channel incised into the sole of the floating tongue. A dramatic thinning, retreat, and speedup began in 1998 and continues today. The timing of the change is coincident with a 1.1°C warming of deep ocean waters entering the fjord after 1997. Assuming a linear relationship between thermal forcing and submarine melt rate, average melt rates should have increased by ~25% (~57 m/yr), sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed.

Greenland and Antarctic ice sheet topography, cavity geometry, and global bathymetry (RTopo-2), links to NetCDF files

The ocean plays an important role in modulating the mass balance of the polar ice sheets by interacting with the ice shelves in Antarctica and with the marine-terminating outlet glaciers in Greenland. Given that the flux of warm water onto the continental shelf and into the sub-ice cavities is steered by complex bathymetry, a detailed topography data set is an essential ingredient for models that address ice-ocean interaction. We followed the spirit of the global RTopo-1 data set and compiled consistent maps of global ocean bathymetry, upper and lower ice surface topographies and global surface height on a spherical grid with now 30-arc seconds resolution. We used the General Bathymetric Chart of the Oceans (GEBCO, 2014) as the backbone and added the International Bathymetric Chart of the Arctic Ocean version 3 (IBCAOv3) and the Interna- tional Bathymetric Chart of the Southern Ocean (IBCSO) version 1. While RTopo-1 primarily aimed at a good and consistent representation of the Antarctic ice sheet, ice shelves and sub-ice cavities, RTopo-2 now also contains ice topographies of the Greenland ice sheet and outlet glaciers. In particular, we aimed at a good representation of the fjord and shelf bathymetry sur- rounding the Greenland continent. We corrected data from earlier gridded products in the areas of Petermann Glacier, Hagen Bræ and Sermilik Fjord assuming that sub-ice and fjord bathymetries roughly follow plausible Last Glacial Maximum ice flow patterns. For the continental shelf off northeast Greenland and the floating ice tongue of Nioghalvfjerdsfjorden Glacier at about 79°N, we incorporated a high-resolution digital bathymetry model considering original multibeam survey data for the region. Radar data for surface topographies of the floating ice tongues of Nioghalvfjerdsfjorden Glacier and Zachariæ Isstrøm have been obtained from the data centers of Technical University of Denmark (DTU), Operation Icebridge (NASA/NSF) and Alfred Wegener Institute (AWI). For the Antarctic ice sheet/ice shelves, RTopo-2 largely relies on the Bedmap-2 product but applies corrections for the geometry of Getz, Abbot and Fimbul ice shelf cavities.

Geochemistry of Globigerinoides ruber from ODP Hole 130-806B

A sea surface temperature (SST) record based on planktonic foraminiferal magnesium/calcium ratios from a site in the western equatorial Pacific warm pool reveals that glacial-interglacial oscillations in SST shifted from a period of 41,000 to 100,000 years at the mid-Pleistocene transition, 950,000 years before the present. SST changes at both periodicities were synchronous with eastern Pacific cold-tongue SSTs but preceded changes in continental ice volume. The timing and nature of tropical Pacific SST changes over the mid-Pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time.