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  • 2015-2019  (63)
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  • 1
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    Low-latitude expressions of high-latitude forcing during Heinrich Stadial 1 and the Younger Dryas in northern South America (2018)
    Elsevier
    In:  Global and Planetary Change, 160 . pp. 1-9.
    Details
    Publication Date: 2021-02-08
    Description: Changes in Atlantic Meridional Overturning Circulation (AMOC) strength exert a major influence on global atmospheric circulation patterns. However, the pacing and mechanisms of low-latitude responses to high-latitude forcing are insufficiently constrained so far. To elucidate the interaction of atmospheric and oceanic forcing in tropical South America during periods of major AMOC reductions (Heinrich Stadial 1 and the Younger Dryas) we generated a high-resolution foraminiferal multi-proxy record from off the Orinoco River based on Ba/Ca and Mg/Ca ratios, as well as stable isotope measurements. The data clearly indicate a three-phased structure of HS1 based on the reconfiguration of ocean currents in the tropical Atlantic Ocean. The initial phase (HS1a) is characterized by a diminished North Brazil Current, a southward displacement of the ITCZ, and moist conditions dominating northeastern Brazil. During subsequent HS1b, the NBC was even more diminished or yet reversed and the ITCZ shifted to its southernmost position. Hence, dryer conditions prevailed in northern South America, while eastern Brazil experienced maximally wet conditions. During the final stage, HS1c, conditions are similar to HS1a. The YD represents a smaller amplitude version of HS1 with a southward-shifted ITCZ. Our findings imply that the low-latitude continental climate response to high-latitude forcing is mediated by reconfigurations of surface ocean currents in low latitudes. Our new records demonstrate the extreme sensitivity of the terrestrial realm in tropical South America to abrupt perturbations in oceanic circulation during periods of unstable climate conditions.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: other
    DOI: 10.1016/j.gloplacha.2017.11.008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Deglacial Heat Uptake by the Southern Ocean and Rapid Northward Redistribution via Antarctic Intermediate Water (2018)
    AGU (American Geophysical Union) | Wiley
    In:  Paleoceanography and Paleoclimatology, 33 (11). pp. 1292-1305.
    Details
    Publication Date: 2021-02-08
    Description: Antarctic Intermediate Water (AAIW) is an important conduit for nutrients to reach the nutrient‐poor low‐latitude ocean areas. In the Atlantic, it forms part of the return path of the Atlantic Meridional Overturning Circulation (AMOC). Despite the importance of AAIW, little is known about variations in its composition and signature during the prominent AMOC and climate changes of the last deglaciation. Here, we reconstruct benthic foraminiferal Mg/Ca‐based intermediate water temperatures (IWTMg/Ca) and intermediate water neodymium (Nd) isotope compositions at sub‐millennial resolution from unique sediment cores located at the northern tip of modern AAIW extent in the tropical W‐Atlantic (850 and 1018 m water depth). Our data indicate a pronounced warming of AAIW in the tropical W‐Atlantic during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). We argue that these warming events were induced by major AMOC perturbations resulting in the pronounced accumulation of heat in the surface Southern Ocean. Combined with published results, our data suggest the subsequent uptake of Southern Ocean heat by AAIW and its rapid northward transfer to the tropical W‐Atlantic. Hence, the rapid deglacial northern climate perturbations directly controlled the AAIW heat budget in the tropical W‐Atlantic after a detour via the Southern Ocean. We speculate that the ocean heat redistribution via AAIW effectively dampened Southern Hemisphere warming during the deglaciation and may therefore have been a crucial player in the climate seesaw mechanisms between the two hemispheres.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1029/2017PA003284
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Pliocene oceanic seaways and global climate (2017)
    Nature Research
    In:  Scientific Reports, 7 (39842).
    Details
    Publication Date: 2020-06-18
    Description: Tectonically induced changes in oceanic seaways had profound effects on global and regional climate during the Late Neogene. The constriction of the Central American Seaway reached a critical threshold during the early Pliocene ~4.8–4 million years (Ma) ago. Model simulations indicate the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) with a signature warming response in the Northern Hemisphere and cooling in the Southern Hemisphere. Subsequently, between ~4–3 Ma, the constriction of the Indonesian Seaway impacted regional climate and might have accelerated the Northern Hemisphere Glaciation. We here present Pliocene Atlantic interhemispheric sea surface temperature and salinity gradients (deduced from foraminiferal Mg/Ca and stable oxygen isotopes, δ18O) in combination with a recently published benthic stable carbon isotope (δ13C) record from the southernmost extent of North Atlantic Deep Water to reconstruct gateway-related changes in the AMOC mode. After an early reduction of the AMOC at ~5.3 Ma, we show in agreement with model simulations of the impacts of Central American Seaway closure a strengthened AMOC with a global climate signature. During ~3.8–3 Ma, we suggest a weakening of the AMOC in line with the global cooling trend, with possible contributions from the constriction of the Indonesian Seaway.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/srep39842
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Subtropical W-Atlantic subsurface warming during deglacial times of reduced Atlantic Meridional Overturning Circulation (2016)
    In:  [Poster] In: 12. International Conference on Paleoceanography (ICP12), 28.08.-02.09.2016, Utrecht, The Netherlands .
    Details
    Publication Date: 2016-09-13
    Description: The Atlantic Meridional Overturning Circulation (AMOC) is intimately linked to abrupt North Atlantic climate change and is a key player for the transport of tropical heat to high northern latitudes. A deglacially reduced AMOC resulted in surface cooling in wide areas of the tropical North Atlantic, while the subsurface ocean experienced regional warming by several degrees due to the reorganization of ocean circulation at intermediate depths (Schmidt et al., 2012). The S-Caribbean (Tobago Basin) is crucial in this respect as several modelling studies predicted substantial subsurface warming during periods of reduced AMOC (Schmidt et al., 2012).We here reconstruct surface and subsurface temperature and salinity changes during the past 30 kyr, based on stable isotope (δ13C, δ18O) and elemental (Mg/Ca) ratios of planktonic surface dwelling (G. ruber) and deep dwelling foraminiferal species, (G. truncatulinoides). The studied sediment core is influenced by cooler and fresher tropical waters during modern circulation conditions. During deglacial times of AMOC slowdowns subsurface waters warmed and became more saline, as the weakened thermohaline circulation allowed Subtropical Gyre waters to enter the tropical W-Atlantic (Chang et al. 2008). Our high resolution data further imply that the inflow of Subtropical Gyre waters into the tropical Atlantic led to the abrupt increase of subsurface temperatures by ~6°C. Such subsurface warming is much higher than the 2.5°C warming proposed by modeling studies. Furthermore, subsurface salinity rose simultaneously with temperatures, pointing to the replacement of cooler/fresher tropical waters by warmer/saltier Subtropical Gyre waters.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 5
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    Rapid deglacial injection of nutrients into the tropical Atlantic via Antarctic Intermediate Water (2017)
    Elsevier
    In:  Earth and Planetary Science Letters, 463 . pp. 118-126.
    Details
    Publication Date: 2020-02-06
    Description: Highlights • First high-resolution Cdw-record from Caribbean intermediate waters. • Rapid nutrient enrichment during HS1 and YD. • Tropical N-Atlantic AAIW nutrient content controlled by Southern Ocean. • Enhanced AAIW nutrient content likely fed low to high latitude productivity. • Dampening of the deglacial global CO2 rise by AAIW nutrient enrichment. As part of the return flow of the Atlantic overturning circulation, Antarctic Intermediate Water (AAIW) redistributes heat, salt, CO2and nutrients from the Southern Ocean to the tropical Atlantic and thus plays a key role in ocean–atmosphere exchange. It feeds (sub)tropical upwelling linking high and low latitude ocean biogeochemistry but the dynamics of AAIW during the last deglaciation remain poorly constrained. We present new multi-decadal benthic foraminiferal Cd/Ca and stable carbon isotope (δ13C) records from tropical W-Atlantic sediment cores indicating abrupt deglacial nutrient enrichment of AAIW as a consequence of enhanced deglacial Southern Ocean upwelling intensity. This is the first clear evidence from the intermediate depth tropical W-Atlantic that the deglacial reconnection of shallow and deep Atlantic overturning cells effectively altered the AAIW nutrient budget and its geochemical signature. The rapid nutrient injection via AAIW likely fed temporary low latitude productivity, thereby dampening the deglacial rise of atmospheric CO2.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2017.01.030
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    The Intermediate Depth Tropical Atlantic Ocean - delayed response to deglacial AMOC perturbations and Subtropical Gyre dynamics (2017)
    In:  [Poster] In: POF-Evaluierung GEOMAR, 04.-06.10.2017, Kiel, Germany .
    Details
    Publication Date: 2017-12-13
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Poster
  • 7
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    South American Hydrological Balance and Paleoceanography during the Late Pleistocene and Holocene (SAMBA) – Cruise No. M125, March 21 – April 15, 2016 - Rio de Janeiro (Brazil) – Fortaleza (Brazil) (2016)
    DFG-Senatskommission für Ozeanographie
    In:  METEOR-Berichte, M125 . DFG-Senatskommission für Ozeanographie, Bremen, 47 pp.
    Details
    Publication Date: 2017-09-15
    Description: R/V METEOR expedition M125 (“SAMBA”) focused on the influence of paleoceanographic changes off NE Brazil on the continental hydrological cycle. For this purpose, we obtained 202 m of gravity (24 stations) and piston cores (9) at seven sections on the shelf and continental slope close to river mouths from Cabo Frio in the south to the Rio Sao Francisco in the north. Coring stations were determined after intensive echosounder surveys (total: 1221 NM). On-board foraminiferal biostratigraphy, as well as color and XRF-scanning already provided first stratigraphic constraints, indicating the preservation of different regional paleoclimatic signals at the respective sections. Based on the preliminary stratigraphy, we retrieved high-resolution archives, covering Holocene sediments on the shelf and late Pleistocene sediments on the slope. These high-resolution archives are complemented by long-term records covering up to 900 ka of continuous sedimentation at deeper sites at smaller rivers. For proxy-calibration and the study of present-day sedimentation dynamics and biogeochemical processes, surface sediments were sampled via multicorer (47), Van Veen Grab (6) and box corer (3). Water samples for determination of the water chemistry (trace elements, stable and radiogenic isotopes) and nutrient composition were retrieved by 55 CTD/Rosette casts. In addition, we run multinet-hauls at seven stations to investigate the planktonic foraminiferal communities in the water column down to 700 m water depth, complemented by filtering water from the ship’s pump twice a day.
    Type: Report , NonPeerReviewed
    Format: text
    DOI: 10.2312/cr_m125
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    OceanRep: Report - Cruise Report
  • 8
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    Loop Current variability - its relation to meridional overturning circulation and the impact of Mississippi discharge (2015)
    Springer
    Details
    Publication Date: 2023-11-08
    Description: The dynamics of the Loop Current (LC) in the Gulf of Mexico (GoM) during transient climates and interglacials, and its interaction with changes in sea level, atmospheric circulation, and Mississippi River (MR) discharge were studied. Geochemical proxy records and numerical modeling indicate that LC eddy shedding and its related heat transport into the GoM increased during the deglaciation. The model simulations imply decreased LC eddy shedding at lowered sea levels, while transports through Yucatan and Florida straits increased due to the southward migration of the Intertropical Convergence Zone (ITCZ) and increased wind-driven transport in the North Atlantic. Consistent with the model, (isotope) geochemical proxy records from the northern GoM show glacial/interglacial amplitudes significantly larger than in the Caribbean and extreme cooling during the Last Glacial Maximum (LGM) due to the vanishing LC eddy shedding. Prominent deglacial melt water releases observed south and west of the MR delta are neither present in the northeastern GoM, nor in sea-surface salinity-records in the subtropical North Atlantic. The freshwater signals were either a regionally restricted phenomenon or due to changes in the isotopic composition of the discharged water. Our results question the impact of MR megadischarges on the large-scale overturning circulation.
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 9
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    Southward displacement of the North Atlantic Subtropical Gyre circulation system during North Atlantic cold spells (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Paleoceanography and Paleoclimatology, 34 (5). pp. 866-885.
    Details
    Publication Date: 2022-01-31
    Description: Key Points: - Rapid subsurface oceanographic change in the tropical W Atlantic reflect shifting Subtropical Gyre - Subsurface warming responds to deglacial AMOC perturbations (Heinrich Stadials 2, 1, and the Younger Dryas) - Southward propagation of Salinity Maximum Water during Northern Hemisphere cold spells shift the mixing zone of tropical and subtropical waters During times of deglacial Atlantic Meridional Overturning Circulation (AMOC) perturbations, the tropical Atlantic experienced considerable warming at subsurface levels. Coupled ocean‐atmosphere simulations corroborate the tight teleconnection between the tropical Atlantic and climate change at high northern latitudes, but still underestimate the relevance of the subsurface N Atlantic Subtropical Gyre (STG) for heat and salt storage and its sensitivity to rapid climatic change. We here reconstruct vertical and lateral temperature and salinity gradients in the tropical W Atlantic and the Caribbean over the last 30 kyrs, based on planktic deep and shallow dwelling foraminiferal Mg/Ca and δ18O‐records. The rapid and large amplitude subsurface changes illustrate a dynamic STG associated with abrupt shifts of North Atlantic hydrographic and atmospheric regimes. During full glacial conditions, the STG has been shifted southward while intensified Ekman‐downwelling associated to strengthened trade winds fostered the formation of warm and saline Salinity Maximum Water (SMW). The southward propagation of SMW was facilitated by the glacially eastward deflected North Brazil Current. During periods of significant AMOC perturbations (Heinrich Stadials 1, and the Younger Dryas), extreme subsurface warming by ~6°C led to diminished lateral subsurface temperature gradients. Coevally, a deep thermocline suggests that SMW fully occupied the subsurface tropical W Atlantic and that the STG reached its southernmost position. During the Holocene, modern‐like conditions gradually developed with the northward retreat of SMW and the development of a strong thermocline ridge between the Subtropical Gyre and the tropical W Atlantic.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018PA003376
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    A new mechanism for millennial scale positive precipitation anomalies over tropical South America (2019)
    Elsevier
    In:  Quaternary Science Reviews, 225 . Art.Nr. 105990.
    Details
    Publication Date: 2022-01-31
    Description: Continental and marine paleoclimate archives from northwestern and northeastern South America recorded positive precipitation anomalies during Heinrich Stadials (HS). These anomalies have been classically attributed to enhanced austral summer (monsoon) precipitation. However, the lack of marine paleoclimate records off eastern South America as well as inconsistencies between southeastern South American continental and marine records hamper a comprehensive understanding of the mechanism responsible for (sub-) tropical South American hydroclimate response to HS. Here we investigate piston core M125-95-3 collected off eastern South America (10.94°S) and simulate South American HS conditions with a high-resolution version of an atmosphere-ocean general circulation model. Further, meridional changes in precipitation over (sub-) tropical South America were assessed with a thorough compilation of previously available marine paleorecords. Our ln(Ti/Ca) and ln(Fe/K) data show increases during HS6-Younger Dryas. It is the first core off eastern South America and the southernmost from the Atlantic continental margin of South America that unequivocally records HS-related positive precipitation anomalies. Based on our new data, model results and the compilation of available marine records, we propose a new mechanism for the positive precipitation anomalies over tropical South America during HS. The new mechanism involves austral summer precipitation increases only over eastern South America while the rest of tropical South America experienced precipitation increases during the winter, challenging the widely held assumption of a strengthened monsoon. South American precipitation changes were triggered by dynamic and thermodynamic processes including a stronger moisture supply from the equatorial North Atlantic (tropical South Atlantic) in austral winter (summer).
    Type: Article , PeerReviewed
    DOI: 10.1016/j.quascirev.2019.105990
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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