Surface sediment characteristics related to provenance and ocean circulation in the Drake Passage sector of the Southern Ocean

Wu, Shuzhuang; Kuhn, Gerhard; Diekmann, Bernhard; Lembke-Jene, Lester; Tiedemann, Ralf; Zheng, Xiaoxu; Ehrhardt, Sophie; Arz, Helge Wolfgang; Lamy, Frank

doi:10.1016/j.dsr.2019.103135

Cited by 25 publications

(31 citation statements)

References 69 publications

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“…from glacial melting during summer (Meredith et al, 2018), additional nutrient input from the APCC and intense mixing at the Peninsula Front. We suggest that high fluctuations in sea ice cover, sea ice thickness and water temperature may stimulate phytoplankton growth rather than stable conditions with very high and long-lasting or low ice cover and/or an ice-free sea surface (e.g., Xiao et al, 2013). We hence strengthen the need to compare the individual concentration records of IPSO 25 and phytoplankton biomarkers rather than using the IPSO 25 (and PIPSO 25 ) record alone to deduce sea ice conditions (see also Müller et al, 2011Müller et al, , 2012.…”

Section: Comparison Of Sea Ice Proxy Records With Modeledmentioning

confidence: 95%

Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study

et al. 2020

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Abstract. In the last decades, changing climate conditions have had a severe impact on sea ice at the western Antarctic Peninsula (WAP), an area rapidly transforming under global warming. To study the development of spring sea ice and environmental conditions in the pre-satellite era we investigated three short marine sediment cores for their biomarker inventory with a particular focus on the sea ice proxy IPSO25 and micropaleontological proxies. The core sites are located in the Bransfield Strait in shelf to deep basin areas characterized by a complex oceanographic frontal system, coastal influence and sensitivity to large-scale atmospheric circulation patterns. We analyzed geochemical bulk parameters, biomarkers (highly branched isoprenoids, glycerol dialkyl glycerol tetraethers, sterols), and diatom abundances and diversity over the past 240 years and compared them to observational data, sedimentary and ice core climate archives, and results from numerical models. Based on biomarker results we identified four different environmental units characterized by (A) low sea ice cover and high ocean temperatures, (B) moderate sea ice cover with decreasing ocean temperatures, (C) high but variable sea ice cover during intervals of lower ocean temperatures, and (D) extended sea ice cover coincident with a rapid ocean warming. While IPSO25 concentrations correspond quite well to satellite sea ice observations for the past 40 years, we note discrepancies between the biomarker-based sea ice estimates, the long-term model output for the past 240 years, ice core records, and reconstructed atmospheric circulation patterns such as the El Niño–Southern Oscillation (ENSO) and Southern Annular Mode (SAM). We propose that the sea ice biomarker proxies IPSO25 and PIPSO25 are not linearly related to sea ice cover, and, additionally, each core site reflects specific local environmental conditions. High IPSO25 and PIPSO25 values may not be directly interpreted as referring to high spring sea ice cover because variable sea ice conditions and enhanced nutrient supply may affect the production of both the sea-ice-associated and phytoplankton-derived (open marine, pelagic) biomarker lipids. For future interpretations we recommend carefully considering individual biomarker records to distinguish between cold sea-ice-favoring and warm sea-ice-diminishing environmental conditions.

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Section: Comparison Of Sea Ice Proxy Records With Modeledmentioning

confidence: 95%

Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study

et al. 2020

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“…In the northern part of the DP, the provenance of terrigenous materials is restricted to proximal source regions, specifically southern Patagonia (Wu et al, 2019). Furthermore, analyses of surface sediments from the eastern South Pacific and DP have excluded a westward dust transport pathway from southern South America dust sources to this region (Wengler et al, 2019), 125 as well as a substantial modern dust contribution from either Patagonia or Australia to the DP (Wu et al, 2019). After the Great Patagonian Glaciation (ca.…”

Section: Study Areamentioning

confidence: 99%

Variations in export production, lithogenic sediment transport and iron fertilization in the Pacific sector of the Drake Passage over the past 400 ka

Toyos

Winckler

Arz

et al. 2021

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Abstract. Changes in Southern Ocean export production have broad biogeochemical and climatic implications. Specifically, iron fertilization likely increased subantarctic nutrient utilization and enhanced the efficiency of the biological pump during glacials. However, past export production in the subantarctic Southeast Pacific is poorly documented, and its connection to Fe fertilization, potentially related to Patagonian Ice Sheet dynamics is unknown. We report on biological productivity changes over the past 400 ka, based on a combination of 230Thxs-normalized and stratigraphy-based mass accumulation rates of biogenic barium, organic carbon, biogenic opal, and calcium carbonate as indicators of paleo-export production in a sediment core upstream of the Drake Passage. In addition, we use fluxes of iron and lithogenic material as proxies for terrigenous matter, and thus potential micronutrient supply. Stratigraphy-based mass accumulation rates are strongly influenced by bottom-current dynamics, which result in variable sediment focussing or winnowing at our site. Carbonate is virtually absent in the core, except during peak interglacial intervals of the Holocene, and Marine Isotope Stages (MIS) 5 and 11, likely caused by transient decreases in carbonate dissolution. All other proxies suggest that export production increased during most glacial periods, coinciding with high iron fluxes. Such augmented glacial iron fluxes at the core site were most likely derived from glaciogenic input from the Patagonian Ice Sheet promoting the growth of phytoplankton. Additionally, glacial export production peaks are also consistent with northward shifts of the Subantarctic and Polar Fronts, which positioned our site south of the Subantarctic Front and closer to silicic acid-rich waters of the Polar Frontal Zone, as well as a with a decrease in the diatom utilization of Si relative to nitrate under Fe-replete conditions. However, glacial export production near the Drake Passage was lower than in the Atlantic and Indian sectors of the Southern Ocean, which may relate to complete consumption of silicic acid in the study area. Our results underline the importance of micro-nutrient fertilization through lateral terrigenous input from South America rather than aeolian transport, and exemplify the role of frontal shifts and nutrient limitation for past productivity changes in the Pacific entrance to the Drake Passage.

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“…The sortable silt mean grain size (SS �� , 10−63 μm) is typically applied for evaluating relative changes in the near-bottom flow speed in deep-sea sediments 23,24 . We correlated near-bottom flow speed mooring measurements with SS �� of seafloor sediments on a north-south Drake Passage transect 25 . However, modern observations reveal that ACC flow speeds are frequently faster than 15 cm/s ; such high speeds can potentially remove parts of the silt and even the sand fractions 23 .…”

Section: Acc Flow Speed Proxies For the Drake Passagementioning

confidence: 99%

“…2C) can reflect changes in sediment fractions by current transport 5,8 , or aeolian input 29 . Major aeolian input can be ruled out in our study area by mineralogical and geochemical properties 25,31,32 .…”

Section: Acc Flow Speed Proxies For the Drake Passagementioning

confidence: 99%

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Orbital- and millennial-scale variability of the Antarctic Circumpolar Current over the past 140,000 years

Lembke‐Jene

Lamy

et al. 2020

Preprint

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The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage over the past 140,000 years, based on grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with reduced ACC intensity during glacials and a more vigorous circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We hypothesize that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations regulated Pacific-Atlantic water exchange via the “cold water route” and affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

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Surface sediment characteristics related to provenance and ocean circulation in the Drake Passage sector of the Southern Ocean

Cited by 25 publications

References 69 publications

Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study

Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study

Variations in export production, lithogenic sediment transport and iron fertilization in the Pacific sector of the Drake Passage over the past 400 ka

Orbital- and millennial-scale variability of the Antarctic Circumpolar Current over the past 140,000 years

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