Sediment Interpretations of Ice Rafted Debris in the Weddell Sea, Antarctica: a 3-3.8 mya Record from ODP Site 697

Abstract

The Pliocene epoch (5.33--2.58 mya) is frequently studied in paleoclimatology because its climate conditions are similar to present and near future scenarios (Federov et al., 2013). Characterizing the stability of the Antarctic ice sheet during the Pliocene is therefore essential for building models on polar ice--sheet & Global Mean Sea Level (GMSL) response to warmer temperatures. Here, we present a sediment record spanning 3--3.8 mya from Ocean Discovery Program (ODP) Site 697 in the Weddell Sea. Ice rafted debris (IRD) provenance and accumulation is analyzed to track potential stability changes in both the West and East Antarctic ice sheets.Site 697 shows large pulses in IRD accumulation in conjunction with peaks in surface ocean productivity from 3.3--3.6 mya, followed by a low IRD accumulation period from 3--3.3 mya. Mineral assemblages and 40 Ar/ 39 Ar dating of ice--rafted hornblendes/biotites links a large IRD component to bedrock eroded from Coats Land (East Antarctica) and subsequent calving from the Filchner Ice Shelf. Icebergs from this source probably traveled a large distance in a Weddell gyre before reaching Site 697, indicating that IRD pulses are of a large magnitude. If these ice--rafting events are originating from fringing ice shelves during Pliocene warmth, it could have large implications for ice sheet stability, highlighting the Weddell Sea embayment as an area of dynamic change.

Climate Change During the Pliocene: Interpretations from Site 697, the Jane Basin, Weddell Sea, Antarctica

“…The samples were then shipped to Wesleyan University where they were washed under standard wet-sieving procedures, and separated into both coarse (greater than 63 microns) and fine (less than 63 microns) fraction groups for analysis. The coarse fraction was utilized for a provenance study of ice-rafted detritus (IRD) using Ar-Ar dating of hornblende and biotite grains (Kaufman, 2016), whereas the fine fraction was used for particle size and compositional analysis. The dry mass of the fine fraction sediment was recorded and further segregated for biosilica removal.…”

“…The weight percent of the coarse fraction was plotted down-core from ~3.78-2.77 Ma (Figure 3-1). (Kaufman, 2016). In addition to calculating the weight percent of the coarse fraction, the Sortable Silt Mean (SS Mean) was calculated, and analyzed down-core (Figure 3-2).…”

“…To resolve whether or not the icebergs traveled a significant distance from their source to the Jane Basin, a provenance analysis of the IRD would be necessary. Kaufman (2016) analyzed the provenance of the IRD in the Jane Basin through Ar-Ar dating of hornblende grains (Figure 4-8 and Table 4-1). Although there appears to be a change in source of the IRD, it is not entirely evident as to whether or not the icebergs were farther-traveled during this time.…”

“…The periods with higher productivity were indicative of an open-ocean allowing for sunlight to penetrate the surface of the ocean, which then allows photosynthetic organisms to thrive. Table 4-2 by Kaufman (2016) provides an interpretation of the productivity with respect to the IRD. However, to further distinguish whether the climate around the Jane Basin was warm or cold, a diatom analysis would likely confirm this speculation by identifying the abundance of icetolerant and ice-intolerant species.…”

“…The IRD within the Jane Basin was interpreted with respect to the productivity in this region based on an analysis of biosilica changes between 3.78-3.03 Ma. The low IRD trend begins at around 3.30 Ma, and was interpreted as time when there was an open-ocean due to a highly productive environment (Kaufman, 2016).…”