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Gottschalk, J, Hodell DA, Skinner LC, Crowhurst SJ, Jaccard SL, Charles C.  2018.  Past carbonate preservation events in the deep southeast Atlantic Ocean (Cape Basin) and their implications for atlantic overturning dynamics and marine carbon cycling. Paleoceanography and Paleoclimatology. 33:643-663.   10.1029/2018pa003353   AbstractWebsite

Micropaleontological and geochemical analyses reveal distinct millennial-scale increases in carbonate preservation in the deep Southeast Atlantic (Cape Basin) during strong and prolonged Greenland interstadials that are superimposed on long-term (orbital-scale) changes in carbonate burial. These data suggest carbonate oversaturation of the deep Atlantic and a strengthened Atlantic Meridional Overturning Circulation (AMOC) during the most intense Greenland interstadials. However, proxy evidence from outside the Cape Basin indicates that AMOC changes also occurred during weaker and shorter Greenland interstadials. Here we revisit the link between AMOC dynamics and carbonate saturation in the deep Cape Basin over the last 400 kyr (sediment cores TN057-21,TN057-10, and Ocean Drilling Program Site 1089) by reconstructing centennial changes in carbonate preservation using millimeter-scale X-ray fluorescence (XRF) scanning data. We observe close agreement between variations in XRF Ca/Ti, sedimentary carbonate content, and foraminiferal shell fragmentation, reflecting a common control primarily through changing deep water carbonate saturation. We suggest that the high-frequency (suborbital) component of the XRF Ca/Ti records indicates the fast and recurrent redistribution of carbonate ions in the Atlantic basin via the AMOC during both long/strong and short/weak North Atlantic climate anomalies. In contrast, the low-frequency (orbital) XRF Ca/Ti component is interpreted to reflect slow adjustments through carbonate compensation and/or changes in the deep ocean respired carbon content. Our findings emphasize the recurrent influence of rapid AMOC variations on the marine carbonate system during past glacial periods, providing a mechanism for transferring the impacts of North Atlantic climate anomalies to the global carbon cycle via the Southern Ocean.

Gruetzner, J, Espejo FJJ, Lathika N, Uenzelmann-Neben G, Hall IR, Hemming SR, LeVay LJ, Barker S, Berke MA, Brentegani L, Caley T, Cartagena-Sierra A, Charles CD, Coenen JJ, Crespin JG, Franzese AM, Han X, Hines SKV, Just J, Koutsodendris A, Kubota K, Norris RD, Santos TP, Robinson R, Rolinson JM, Simon MH, Tangunan D, van der Lubbe HJL, Yamane M, Zhang H, Expedition S.  2019.  A new seismic stratigraphy in the Indian-Atlantic Ocean gateway resembles major paleo-oceanographic changes of the last 7 Ma. Geochemistry Geophysics Geosystems. 20:339-358.   10.1029/2018gc007668   AbstractWebsite

The exchange of water masses between the Indian Ocean and the Atlantic constitutes an integral interocean link in the global thermohaline circulation. Long-term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late Miocene onward. Here we present results from International Ocean Discovery Program Site U1475 (Agulhas Plateau) located over a sediment drift proximal to the entrance of North Atlantic Deep Water into the Southern Ocean and South Indian Ocean. Site U1475 comprises a complete carbonate-rich stratigraphic section of the last similar to 7 Ma that provides an archive of climate-induced variations in ocean circulation. Six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time. The formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition. Synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy. Prominent reflectors are related to late Pleistocene glacial/interglacial variability, the middle and early Pleistocene transitions, and the onset of the northern hemisphere glaciation. A peculiar early Pliocene interval (similar to 5.3-4.0 Ma) bounded by two reflectors is characterized by fourfold elevated sedimentation rates (> 10 cm/kyr) and the occurrence of sediment waves. We argue that this enhanced sediment transport to the Agulhas Plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of North Atlantic Deep Water.

Guilderson, TP, Fallon S, Moore MD, Schrag DP, Charles CD.  2009.  Seasonally resolved surface water Delta C-14 variability in the Lombok Strait: A coralline perspective. Journal of Geophysical Research-Oceans. 114   10.1029/2008jc004876   AbstractWebsite

We have explored surface water mixing in the Lombok Strait through a bimonthly resolved surface water Delta C-14 time series reconstructed from a coral in the Lombok Strait that spans 1937 through 1990. The prebomb surface water Delta C-14 average is -60.5 parts per thousand and individual samples range from -72 parts per thousand to 134 parts per thousand. The annual average postbomb maximum occurs in 1973 at 122 parts per thousand The timing of the postbomb maximum is consistent with a primary subtropical source for the surface waters in the Indonesian seas. During the postbomb period, the coral records regular seasonal cycles of 5 parts per thousand to 20 parts per thousand. Seasonal high Delta C-14 occur during March-May (warm, low salinity), and low Delta C-14 occur in September (cool, higher salinity). The Delta C-14 seasonality is coherent and in phase with the seasonal Delta C-14 cycle observed in Makassar Strait. We estimate the influence of high Delta C-14 Makassar Strait (North Pacific) water flowing through the Lombok Strait using a two end-member mixing model and the seasonal extremes observed at the two sites. The percentage of Makassar Strait water varies between 16 parts per thousand and 70 parts per thousand, and between 1955 and 1990, it averages at 40 parts per thousand. The rich Delta C-14 variability has a biennial component reflecting remote equatorial Indian Ocean forcing and a component in the ENSO band, which is interpreted to reflect Pacific forcing on the Delta C-14 signature in Lombok Strait.