Browsing by Author "Riesselman, CR"

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    Late glacial and Holocene climate change in the subantarctic Auckland Islands
    (American Geophysical Union (AGU), 2017-12-14) Gilmer, G; Moy, CM; Vandergoes, MJ; Gadd, PS; Riesselman, CR; Jacobsen, GE; Wilson, GS; Visinand, C
    Situated within the core of the Southern Hemisphere westerly winds, and between the subtropical and subantarctic fronts, the New Zealand subantarctic islands are uniquely positioned to evaluate past ocean and atmospheric change in the middle to high southern latitudes. We collected a series of sediment cores from Auckland Island fjords to produce a high-resolution record of climate change following the Last Glacial Maximum. Physical property and organic geochemical data, Itrax XRF, and visual core descriptions indicate the cores capture several phases of sedimentation. From these studies, we identify four primary sedimentary facies: 1) a deglacial facies exhibiting mm-scale laminae defined by magnetic susceptibility and density contrasts and high counts of elements associated with terrigenous sources; 2) a lacustrine facies defined by very low density, high organic carbon concentrations and low counts of lithophilic elements; 3) a marine transgression facies with moderate density, moderate bioturbation and alternating marine and lacustrine sedimentary components; 4) a marine facies that contains biogenic carbonate. Radiocarbon results indicate deglacial sedimentation was underway in the basin by approximately 19,000 cal yr BP. Lacustrine deposition in ice-free conditions began around 15,600 cal yr BP and continued until marine transgression at approximately 9,500 cal yr BP. During the early Holocene between 11 and 9.5 ka, we observe elevated n-alkane δD values and an overall increase in redox-sensitive elements that signal a combination of warmer atmospheric temperatures and reduced westerly wind strength that drives fjord stratification. Poleward-shifted westerlies south of the Auckland Islands could accommodate these results, but there are few records to corroborate this interpretation. We will discuss these results within the context of developing New Zealand and subantarctic paleoclimate records in order to provide a more comprehensive record of past change.
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    Late Pleistocene and Holocene climate and environmental evolution of a subantarctic fjord ingression basin in the southwest Pacific
    (Elsevier, 2021-02-01) Greer, G; Moy, CM; Riesselman, CR; Vandergoes, MJ; Jacobsen, GE; Gorman, AR; Tidey, EJ; Wilson, GS
    Subantarctic islands are located at a critical latitude for reconstructing past changes in ocean-atmosphere interactions. Currently, there is a lack of high-resolution records from the Pacific sector of the Southern Ocean that can be used to reconstruct climate since the Last Glacial Maximum (LGM). Here, we present a reconstruction of environmental change from a fjord ingression basin at New Zealand’s subantarctic Auckland Islands (50.5°S) over the last ∼19 ka cal BP. Using sedimentological and geochemical analysis of cores collected along a depth transect in Norman Inlet we find evidence for four different stages of environmental history: deglacial, lacustrine, marine transgression, and marine. Glaciers retreated from their maximum extent before 19.4 ka cal BP during a period of ice retreat that appears synchronous across the Pacific basin, likely due to southward migration of the Subtropical Front. However, in contrast to other glaciated regions, we see no evidence for ice re-advance, and a proglacial lake was present in the basin until 15.7 ka cal BP. Following deglaciation, organic-rich sedimentation dominated the lacustrine environment until post-glacial sea-level rise flooded the depositional basin at 8.8 ka cal BP. Deposition of organic-rich sediment continued during the Antarctic Cold Reversal and we find no evidence for a glacial re-advance. Mixing of terrestrial and marine organic matter during the marine transgression (8.8–6.7 ka cal BP) indicates significant erosion and re-working of sediment in the catchment as seawater overtopped the sill. Modern fjord circulation commenced ∼6.7 ka cal BP when sea level reached its maximum in the early Holocene. This well-dated, high-resolution record constrains the timing of deglaciation, sea-level rise, and subantarctic environmental change following the LGM that expands our understanding of the key drives of climate change in the middle to high southern latitudes. © 2020 Elsevier Ltd.