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  • 1
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    Arctic Ocean evidence for late Quaternary initiation of northern Eurasian ice sheets (1997)
    GSA, Geological Society of America
    In:  Geology, 25 (9). pp. 783-786.
    Details
    Publication Date: 2017-04-10
    Description: A high-resolution multiparameter stratigraphy allows the identification of late Quaternary glacial and interglacial cycles in a central Arctic Ocean sediment core. Distinct sandy layers in the upper part of the otherwise fine-grained sediment core from the Lomonosov Ridge (lat 87.5°N) correlate to four major glacials since ca. 0.7 Ma. The composition of these ice-rafted terrigenous sediments points to a glaciated northern Siberia as the main source. In contrast, lithic carbonates derived from North America are also present in older sediments and indicate a northern North American glaciation since at least 2.8 Ma. We conclude that large-scale northern Siberian glaciation began much later than other Northern Hemisphere ice sheets.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/0091-7613(1997)​025〈0783:AOEFLQ〉​2.3.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Discovery of Miocene to early Pleistocene deposits on Mayaguana, Bahamas: Evidence for recent active tectonism on the North American margin (2011)
    GSA, Geological Society of America
    In:  Geology, 39 (6). pp. 523-526.
    Details
    Publication Date: 2017-05-18
    Description: We report here the discovery of Miocene, Pliocene, and early Pleistocene shallow-marine carbonates on Mayaguana Island (southeastern Bahamas) that have so far not been observed on any other Bahamian island. Spanning more than 17 m.y., but 〈12 m thick, this stratigraphic succession only occurs along the northern coast of the island, indicating that the Mayaguana Bank underwent minor subsidence throughout the late Cenozoic and was tilted toward the south during the Quaternary. In addition to considerably extending the stratigraphic record of the Bahamas Islands, our findings demonstrate that these carbonate banks were at different elevations and subsided at different rates during the Neogene. The young age of the tilting event detected on Mayaguana further shows that parts of the southeastern margin of North America have recently undergone tectonic activity a long way from its actual boundary with the Caribbean plate.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G32011.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Dolomite formation within the methanogenic zone induced by tectonically driven fluids in the Peru accretionary prism (2011)
    GSA, Geological Society of America
    In:  Geology, 39 (6). pp. 563-566.
    Details
    Publication Date: 2017-07-28
    Description: Early diagenetic dolomite formation in methanogenic marine sediments is enigmatic because acidifi cation by CO2, a by-product of methanogenesis, should lead to carbonate dissolution and not precipitation. However, petrographic relationships indicate that dolomite breccia layers with δ13C values of ~+15‰, recovered from the lower slope of the Peru continental margin (Ocean Drilling Program Site 1230), formed deep in the methanogenic zone during tectonic activity of a décollement. Based on radiogenic Sr isotope ratios (87Sr/86Sr 〉 0.711) and positive δ18O values (+6‰), we present evidence that the dolomite breccias mainly formed from fl uids originating from deep sedimentary units within the accretionary prism, where they interacted with continental crust and/or siliciclastic rocks of continental affi nity. Due to silicate alteration and dehydration, such fl uids are likely alkaline and thus have the potential to neutralize the acidifi cation imposed by the high dissolved CO2 concentrations. This scenario provides a potential mechanism by which dolomite formation can be induced deep in a highly active methanogenic zone.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G31810.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Northern Sourced Water dominated the Atlantic Ocean during the Last Glacial Maximum (2020)
    GSA (Geological Society of America)
    Details
    Publication Date: 2023-02-08
    Description: Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO2 concentrations. Remineralized carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here, we present new sediment-derived bottom-water neodymium isotope records that allow fingerprinting of water masses and provide a more complete picture of the Atlantic Meridional Overturning Circulation geometry during the Last Glacial Maximum. These results suggest that the vertical and meridional structure of the Atlantic water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern-sourced water substantially expanding to shallower depths and farther into the Northern Hemisphere than today, which had been previously inferred from stable carbon isotope (δ13C) reconstructions. We argue that depleted δ13C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern-sourced water. Instead, these values may represent a northern-sourced water mass with lower than modern preformed δ13C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation, corroborating previous evidence.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    A major and long-term Pliocene intensification of the Mediterranean Outflow, 3.5-3.3 Ma ago (2009)
    GSA, Geological Society of America
    In:  Geology, 37 (9). pp. 811-814.
    Details
    Publication Date: 2017-05-24
    Description: Largely continuous millennial-scale records of benthic delta O-18, Mg/Ca-based temperature, and salinity variations in bottom waters were obtained from Deep Sea Drilling Project (DSDP) Site 548 (East Atlantic continental margin near Ireland, 1250 m water depth) for the period 3.7-3.0 Ma ago. High epsilon(Nd) values of -10.7 to -9 show that this site monitored changes in Mediterranean Outflow Water (MOW) throughout the mid-Pliocene. Bottom water variability at Ocean Drilling Progam (ODP) Site 978 (Alboran Sea, 1930 m water depth) provides a complementary record of MOW composition near its West Mediterranean source. Both sites show a singular and persistent rise in bottom water salinities by 0.7-1.4 psu, and in densities by similar to 1 kg m(-3) from 3.5 to 3.3 Ma ago, which is matched by an similar to 3 degrees C increase in bottom water temperature at Site 548. This event suggests the onset of strongly enhanced deep-water convection in the Mediterranean Sea and a related increase in MOW flow as a result of major aridification in the Mediterranean source region. In harmony with model suggestions, the enhanced MOW flow has possibly intensified Upper North Atlantic Deep Water formation.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G30058A.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Nd and Pb isotopes in Atlantic and Pacific water masses before and after closure of the Panama Gateway (1999)
    GSA, Geological Society of America
    In:  Geology, 27 . pp. 1147-1150.
    Details
    Publication Date: 2017-09-26
    Description: Two Nd and Pb isotope time series of hydrogenous ferromanganese crusts, one from the Tehuantepec Ridge in the deep eastern equatorial Pacific and the other from Blake Plateau in the shallow northwestern Atlantic, which cover the past 7–8 m.y., show no variations coincident with the final closure of the Panama gateway, estimated as ca. 3.5 Ma. The record of the Atlantic crust located in the present-day Gulf Stream shows a shift in isotope composition from ca. 8 to 5 Ma that is explained by a diminishing supply of Pacific water. It is argued that the major restriction of water-mass exchange through the Panama gateway occurred before 5 Ma and thus cannot serve as a direct cause of the onset of Northern Hemisphere glaciation. The absence of a significant signature in the isotope records from the Pacific crust suggests that the volume of water exchanged with the Atlantic through shallow archipelagic straits of the gateway during the 3–4 m.y. prior to closure was too small to influence the radiogenic isotope composition of Pacific deep water.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/0091-7613(1999)027〈1147:NAPIIA〉2.3.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    The impact of postdepositional alteration on iron- and molybdenum-based redox proxies (2021)
    GSA (Geological Society of America)
    Details
    Publication Date: 2024-02-07
    Description: Ratios of (un)reactive iron species, authigenic molybdenum contents (Moauth), and molybdenum isotope compositions (δ98Moauth) in sedimentary rocks are geochemical proxies that are widely used to reconstruct past marine redox states, which have been calibrated in modern marine settings covering oxic to euxinic conditions. However, syn- and postdepositional processes can result in alterations and ambiguities of proxy-derived redox signals that can challenge the validity of paleoreconstructions. We present new data from modern organic-rich sediments of two oxygen minimum zone settings in the Gulf of California and the Peruvian margin. The results show that Mo is fully immobilized shortly after deposition by reaction with hydrogen sulfide (H2S) produced during organoclastic sulfate reduction. Thus, any H2S produced deeper in the sediment (e.g., by sulfate reduction coupled to anaerobic methane oxidation) leaves the initially deposited Mo concentrations and δ98Mo signatures unaltered, which supports the robustness of Mo-based redox proxies. In contrast, the Fe speciation data reveal continued pyritization due to constant exposure of Fe minerals to H2S. Importantly, both Fe bound to oxides and carbonates (highly reactive Fe) and also poorly reactive Fe (e.g., sheet silicates) undergo pyritization during early diagenesis. This process generates Fe-based proxy signatures that falsely imply ferruginous or euxinic conditions.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    The early opening of the Equatorial Atlantic gateway and the evolution of Cretaceous peak warming (2023)
    GSA (Geological Society of America)
    Details
    Publication Date: 2024-02-07
    Description: The Cretaceous opening of the Equatorial Atlantic gateway (EAG) is considered a driver of major changes in global oceanography, carbon cycling, and climate. However, the early stages of EAG opening are poorly understood. We present seawater Nd-isotope, bulk geochemical, and micropaleontological data from two South Atlantic drill cores that constrain the onset of shallow (〈500 m) and intermediate (〈~1000 m) water mass exchange across the EAG to 113 Ma and 107 Ma, respectively. Deep water mass exchange (>2000 m) was enabled by at least ca. 100 Ma, as much as 10 m.y. earlier than previously estimated. In response to EAG opening, deep-water ventilation in the South Atlantic, North Atlantic, and Tethys basins intensified, thereby triggering basin-scale reductions in organic carbon burial. We propose that the consequent drop in carbon sequestration in concert with increased atmospheric CO2 fluxes from subduction zones acted as major amplifiers of global warming that culminated in peak greenhouse conditions during the mid-Cretaceous.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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