In:
Climate of the Past, Copernicus GmbH, Vol. 16, No. 4 ( 2020-07-16), p. 1245-1261
Abstract:
Abstract. The number of sedimentary records collected along the
Brazilian continental margin has increased significantly in recent years,
but relatively few are located in shallow waters and register
paleoceanographic processes in the outer shelf–middle slope prior to 10–15 ka. For instance, the northward flow up to 23–24∘ S of
cold and fresh shelf waters sourced from the Subantarctic region is an
important feature of current hydrodynamics in the subtropical western South
Atlantic Ocean, and yet limited information is available for the long-term
changes of this system. Herein, we considered a suite of organic and
inorganic proxies – alkenones-derived sea surface temperature (SST),
δD-alkenones, δ18O of planktonic foraminifera, and
ice-volume free seawater δ18OIVF−SW – in sediment from
two cores (RJ-1501 and RJ-1502) collected off the Rio de Janeiro Shelf (SE
Brazilian continental shelf) to shed light on SST patterns and relative
salinity variations since the end of the last glacial cycle in the region
and the implications of these processes over a broader spatial scale. The
data indicate that, despite the proximity (∼40 km apart) of
both cores, apparently contradictory climatic evolution occurred at the two
sites, with the shallower (deeper) core RJ-1501 (RJ-1502) showing
consistently cold (warm) and fresh (salt) conditions toward the Last Glacial Maximum (LGM) and last deglaciation. This can be reconciled by considering that the RJ-1501 core registered a signal from mid- to high latitudes on the upper slope off Rio de Janeiro represented by the influence of the cold and fresh waters composed of Subantarctic Shelf Water and La Plata Plume Water transported northward by the Brazilian Coastal Current (BCC). The data from core RJ-1502 and previous information for deep-cores from the same region
support this interpretation. In addition, alkenone-derived SST and δ18OIVF−SW suggest a steep thermal and density gradient formed
between the BCC and Brazil Current (BC) during the last climate transition
which, in turn, may have generated perturbations in the air–sea heat flux
with consequences for the regional climate of SE South America. In a
scenario of future weakening of the Atlantic Meridional Overturning
Circulation, the reconstructed gradient may become a prominent feature of
the region.
Type of Medium:
Online Resource
ISSN:
1814-9332
DOI:
10.5194/cp-16-1245-2020
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2217985-9
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