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Thermal response of the western tropical Atlantic to slowdown of the Atlantic Meridional Overturning Circulation

Texto completo
Crivellari, Stefano [1, 2] ; Chiessi, Cristiano Mazur [1] ; Kuhnert, Henning [3] ; Haeggi, Christoph [3, 4] ; Mollenhauer, Gesine [5] ; Hefter, Jens [5] ; Portilho-Ramos, Rodrigo [3] ; Schefuss, Enno [3] ; Mulitza, Stefan [3]
Número total de Autores: 9
Afiliação do(s) autor(es):
[1] Univ Sao Paulo, Sch Arts Sci & Humanities, Sao Paulo - Brazil
[2] Univ Sao Paulo, Inst Geosci, Sao Paulo - Brazil
[3] Univ Bremen, MARUM Ctr Marine Environm Sci, Bremen - Germany
[4] Univ Southern Calif, Dept Earth Sci, Los Angeles, CA - USA
[5] Alfred Wegener Inst Polar & Marine Res, Bremerhaven - Germany
Número total de Afiliações: 5
Tipo de documento: Artigo Científico
Fonte: Earth and Planetary Science Letters; v. 519, p. 120-129, AUG 1 2019.
Citações Web of Science: 0

The western tropical Atlantic plays an important role in the interhemispheric redistribution of heat during millennial-scale changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC). The proper evaluation of this role depends on a clear understanding of sea surface temperature (SST) variations during AMOC slowdown periods like Heinrich Stadials (HS) in the western tropical Atlantic. However, published SST records from the western tropical Atlantic between ca. 4 degrees S and 7 degrees N show inconsistencies that are apparently related to the employed temperature proxy (i.e., Mg/Ca versus alkenone unsaturation index U-37(k')). In general, while Mg/Ca values indicate warming during Heinrich Stadials, U-37(k') values show cooling. To assess this issue, we sampled core GeoB16224-1 retrieved off French Guiana (i.e., 6 degrees 39.38'N) and reconstructed water temperatures at high resolution using Mg/Ca on the foraminifera species Globigerinoides ruber, U-37(k'), TEX86 and modern analogue technique (MAT) transfer functions using planktonic foraminifera assemblages calibrated for 50 m water depth. Our results show that Mg/Ca and TEX86 values recorded an increase in SST related to AMOC slowdown. Conversely, U-37(k') and MAT values registered a decrease in temperatures during HS3 and HS1. Our U-37(k') and Mg/Ca results thus confirm the previously reported inconsistency for the period between 48-13 cal ka BP. We suggest that several non-thermal physiological effects probably imparted a negative temperature bias on the U-37(k') temperatures during Heinrich Stadials. However, MAT-based temperatures show similar variability with U-37(k')-based temperatures. Hence, we also suggest that during severe slowdown periods of the AMOC, a steeper meridional temperature gradient together with a southward shift of the Intertropical Convergent Zone produced not only an increase in SST but also a stronger upper water column stratification and a shoaling of the thermocline, decreasing subsurface temperatures. Our new high resolution temperature records allow a better characterization of the thermal response of the upper water column in the tropical western Atlantic to slowdown events of the AMOC, reconciling previously discrepant records. (C) 2019 Elsevier B.V. All rights reserved. (AU)

Processo FAPESP: 13/22521-2 - Efeitos das mudanças abruptas da circulação meridional do Atlântico sobre as massas de água profunda: uma abordagem isotópica
Beneficiário:Stefano Crivellari
Linha de fomento: Bolsas no Brasil - Doutorado Direto
Processo FAPESP: 12/17517-3 - Resposta da porção oeste do Oceano Atlântico às mudanças na circulação meridional do Atlântico: variabilidade milenar a sazonal
Beneficiário:Cristiano Mazur Chiessi
Linha de fomento: Auxílio à Pesquisa - Programa de Pesquisa sobre Mudanças Climáticas Globais - Jovens Pesquisadores