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  • 1
    Publikationsdatum: 2020-02-06
    Beschreibung: We present the first subprecessional record of seawater 87Sr/86Sr isotope ratios for a marginal Mediterranean subbasin. The sediments contained in this interval (three precessional cycles between 6.60 and 6.55 Ma) are important because they record conditions during the transition to the Messinian Salinity Crisis (MSC; 5.97 to 5.33 Ma), an event for which many details are still poorly understood. The record, derived from planktic foraminifera of the late Miocene Sorbas Basin (SE Spain), shows brief excursions with precessional cyclicity to 87Sr/86Sr ratios higher than coeval ocean 87Sr/86Sr. The hydrologic conditions required to generate the observed record are investigated using box modeling, constrained using a new paleodepth estimate (150 to 250 m) based on benthic foraminiferal assemblages. The box model results highlight the role of climate-driven interbasin density contrast as a significant driver of, or impediment to, exchange. The results are particularly significant in the context of the MSC, where 87Sr/86Sr excursions have been interpreted purely as a consequence of physical restriction. To replicate the observed temporal patterns of lithological variations and 87Sr/86Sr isotope excursions, the Sorbas Basin “box” must have a mainly positive hydrologic budget, in contrast with the Mediterranean's negative budget during the late Miocene. This result has implications for the assumption of synchronous deposition of specific sedimentary layers (sapropels) between marginal and open Mediterranean settings at subprecessional resolution. A net positive hydrologic budget in marginal Mediterranean subbasins may reconcile observations of freshwater inclusions in gypsum deposits.
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Publikationsdatum: 2015-12-18
    Beschreibung: Marine gateways play a critical role in the exchange of water, heat, salt and nutrients between oceans and seas. As a result, changes in gateway geometry can significantly alter both the pattern of global ocean circulation and associated heat transport and climate, as well as having a profound impact on local environmental conditions. Mediterranean-Atlantic marine corridors that pre-date the modern Gibraltar Strait, closed during the Late Miocene and are now exposed on land in northern Morocco and southern Spain. The restriction and closure of these Miocene connections resulted in extreme salinity fluctuations in the Mediterranean, leading to the precipitation of thick evaporites. This event is known as the Messinian Salinity Crisis (MSC). The evolution and closure of the Mediterranean-Atlantic gateways are a critical control on the MSC, but at present the location, geometry and age of these gateways are still highly controversial, as is the impact of changing Mediterranean outflow on Northern Hemisphere circulation. Here, we present a comprehensive overview of the evolution of the Late Miocene gateways and the nature of Mediterranean-Atlantic exchange as deduced from published studies focussed both on the sediments preserved within the fossil corridors and inferences that can be derived from data in the adjacent basins. We also consider the possible impact of evolving exchange on both the Mediterranean and global climate and highlight the main enduring challenges for reconstructing past Mediterranean-Atlantic exchange.
    Materialart: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Publikationsdatum: 2023-02-08
    Beschreibung: The Atlantic meridional overturning circulation (AMOC) represents the zonally integrated stream function of meridional volume transport in the Atlantic Basin. The AMOC plays an important role in transporting heat meridionally in the climate system. Observations suggest a heat transport by the AMOC of 1.3 PW at 26°N—a latitude which is close to where the Atlantic northward heat transport is thought to reach its maximum. This shapes the climate of the North Atlantic region as we know it today. In recent years there has been significant progress both in our ability to observe the AMOC in nature and to simulate it in numerical models. Most previous modeling investigations of the AMOC and its impact on climate have relied on models with horizontal resolution that does not resolve ocean mesoscale eddies and the dynamics of the Gulf Stream/North Atlantic Current system. As a result of recent increases in computing power, models are now being run that are able to represent mesoscale ocean dynamics and the circulation features that rely on them. The aim of this review is to describe new insights into the AMOC provided by high-resolution models. Furthermore, we will describe how high-resolution model simulations can help resolve outstanding challenges in our understanding of the AMOC.
    Materialart: Article , PeerReviewed
    Format: text
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Publikationsdatum: 2020-02-10
    Beschreibung: The Atlantic meridional overturning circulation (AMOC) represents the zonally integrated stream function of meridional volume transport in the Atlantic Basin. The AMOC plays an important role in transporting heat meridionally in the climate system. Observations suggest a heat transport by the AMOC of 1.3 PW at 26°N ‐ a latitude which is close to where the Atlantic northward heat transport is thought to reach its maximum. This shapes the climate of the North Atlantic region as we know it today. In recent years there has been significant progress both in our ability to observe the AMOC in nature and to simulate it in numerical models. Most previous modeling investigations of the AMOC and its impact on climate have relied on models with horizontal resolution that does not resolve ocean mesoscale eddies and the dynamics of the Gulf Stream/North Atlantic Current system. As a result of recent increases in computing power, models are now being run that are able to represent mesoscale ocean dynamics and the circulation features that rely on them. The aim of this review is to describe new insights into the AMOC provided by high‐resolution models. Furthermore, we will describe how high‐resolution model simulations can help resolve outstanding challenges in our understanding of the AMOC.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    Publikationsdatum: 2019-10-01
    Beschreibung: Over the last decade, our understanding of cli- mate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most likely out of equi- librium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geolog- ical records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitiv- ity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
    Standort Signatur Einschränkungen Verfügbarkeit
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