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  • GEOTRACES; Global marine biogeochemical cycles of trace elements and their isotopes  (2)
  • South Asian monsoon  (2)
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  • 1
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    Persistent Provenance of South Asian Monsoon‐Induced Silicate Weathering Over the Past 27 Million Years (2021)
    Details
    Publication Date: 2021-07-21
    Description: The development of the South Asian monsoon (SAM) and Himalaya‐Tibetan Plateau uplift were closely intertwined with some studies suggesting that uplift initiated the monsoon whereas others link tectonics with monsoon‐controlled exhumation. Silicate weathering controls atmospheric CO2 on geological timescales resulting in a large potential for monsoon strength and the Himalayan orogeny to influence global climate but detailed records of SAM‐induced weathering on million year (Myr) timescales are lacking. Here, we present radiogenic Sr, Nd, and Pb isotope compositions of clay minerals produced by silicate weathering and transported to the central Bay of Bengal. The radiogenic isotope data exhibit a relatively small range and demonstrate a remarkably consistent mixture of sources dominated by Himalayan rocks and the Indo‐Burman ranges, which consist of sediments derived from the Himalayas. This suggests that the spatial pattern of regional weathering, which today is highest in the regions of strongest monsoon rains, has persisted in a similar form for the last 27 Myrs. A pronounced increase in primary clay mineral abundance (from 9% to 22%) coincident with global cooling 13.9 Myrs ago points to a shift in the weathering regime given that the clay provenance did not change dramatically. Relatively weaker chemical weathering intensity during the mid and late Miocene cooling suggests increased aridity and changes in the large scale atmospheric circulation in the SAM domain. The establishment of the dry winter monsoon season during the mid and late Miocene may have caused this shift in the weathering regime and can reconcile much of the contrasting evidence for SAM initiation.
    Description: Key Points: Relatively stable mixture of source rocks weathered to clays over the past 27 Myrs Pronounced increase in primary clay minerals occurred 13.9 Myrs ago Shift in weathering regime possibly result of winter monsoon dry season development
    Keywords: 551.3 ; Bay of Bengal ; clay minerals ; radiogenic Sr, Nd, Pb isotopes ; Silicate silicate weathering ; South Asian monsoon
    Type: article
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    CITATION GEO-LEO
  • 2
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    South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 16 (2015): 505–521, doi:10.1002/2014GC005586.
    Description: The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial-interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay-size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval εNd values changed little, generally oscillating between −7.3 and −5.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo-Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite + chlorite) ratios (up to 14), as well as low 87Sr/86Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite-poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short-term northern Atlantic climate variability on millennial time scales.
    Description: Part of this work was funded by German Science Foundation (DFG), grant HA5751/3-1.
    Description: 2015-08-24
    Keywords: Marine sediments ; Clay minerals ; Radiogenic isotopes ; Andaman Sea ; South Asian monsoon
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/msword
    Format: application/pdf
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    PAPER (OA)
  • 3
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    Hafnium and neodymium in surface waters of the Atlantic sector of the Southern Ocean (2012)
    PANGAEA
    In:  Supplement to: Stichel, Torben; Frank, Martin; Rickli, Jörg Dominik; Hathorne, Ed C; Haley, Brian A; Jeandel, Catherine; Pradoux, Catherine (2012): Sources and input mechanisms of hafnium and neodymium in surface waters of the Atlantic sector of the Southern Ocean. Geochimica et Cosmochimica Acta, 94, 22-37, https://doi.org/10.1016/j.gca.2012.07.005
    Details
    Publication Date: 2023-02-24
    Description: Radiogenic isotopes of hafnium (Hf) and neodymium (Nd) are powerful tracers for water mass transport and trace metal cycling in the present and past oceans. However, due to the scarcity of available data the processes governing their distribution are not well understood. Here we present the first combined dissolved Hf and Nd isotope and concentration data from surface waters of the Atlantic sector of the Southern Ocean. The samples were collected along the Zero Meridian, in the Weddell Sea and in the Drake Passage during RV Polarstern expeditions ANT-XXIV/3 and ANT-XXIII/3 in the frame of the International Polar Year (IPY) and the GEOTRACES program. The general distribution of Hf and Nd concentrations in the region is similar. However, at the northernmost station located 200 km southwest of Cape Town a pronounced increase of the Nd concentration is observed, whereas the Hf concentration is minimal, suggesting much less Hf than Nd is released by the weathering of the South African Archean cratonic rocks. From the southern part of the Subtropical Front (STF) to the Polar Front (PF) Hf and Nd show the lowest concentrations (〈0.12 pmol/kg and 10 pmol/kg, respectively), most probably due to the low terrigenous flux in this area and efficient scavenging of Hf and Nd by biogenic opal. In the vicinity of landmasses the dissolved Hf and Nd isotope compositions are clearly labelled by terrigenous inputs. Near South Africa Nd isotope values as low as epsilon-Nd = -18.9 indicate unradiogenic inputs supplied via the Agulhas Current. Further south the isotopic data show significant increases to epsilon-Hf = 6.1 and epsilon-Nd = -4.0 documenting exchange of seawater Nd and Hf with the Antarctic Peninsula. In the open Southern Ocean the Nd isotope compositions are relatively homogeneous (epsilon-Nd ~ -8 to -8.5) towards the STF, within the Antarctic Circumpolar Current, in the Weddell Gyre, and the Drake Pasage. The Hf isotope compositions in the entire study area only show a small range between epsilon-Hf = +6.1 and +2.8 support Hf to be more readily released from young mafic rocks compared to old continental ones. The Nd isotope composition ranges from epsilon-Nd = -18.9 to -4.0 showing Nd isotopes to be a sensitive tracer for the provenance of weathering inputs into surface waters of the Southern Ocean.
    Keywords: GEOTRACES; Global marine biogeochemical cycles of trace elements and their isotopes
    Type: Dataset
    Format: application/zip, 3 datasets
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    DATA PANGAEA
  • 4
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    Analysis of Nd isotope, REE and oxygen isotope ratios on water samples across Fram Strait (2017)
    PANGAEA
    In:  Supplement to: Laukert, Georgi; Frank, Martin; Bauch, Dorothea; Hathorne, Ed C; Rabe, Benjamin; von Appen, Wilken-Jon; Wegner, Carolyn; Zieringer, Moritz; Kassens, Heidemarie (2017): Ocean circulation and freshwater pathways in the Arctic Mediterranean based on a combined Nd isotope, REE and oxygen isotope section across Fram Strait. Geochimica et Cosmochimica Acta, 202, 285-309, https://doi.org/10.1016/j.gca.2016.12.028
    Details
    Publication Date: 2023-04-03
    Description: The water masses passing the Fram Strait are mainly responsible for the exchange of heat and freshwater between the Nordic Seas and the Arctic Ocean (the Arctic Mediterranean, AM). Disentangling their exact sources, distribution and mixing, however, is complex. This work provides new insights based on a detailed geochemical tracer inventory including dissolved Nd isotope (e-Nd), rare earth element (REE) and stable oxygen isotope (d18O) data along a full water depth section across Fram Strait. We find that Nd isotope and REE distributions in the open AM primarily reflect lateral advection of water masses and their mixing. Seawater-particle interactions exert important control only above the shelf regions, as observed above the NE Greenland Shelf. Advection of northward flowing warm Atlantic Water (AW) is clearly reflected by an e-Nd signature of -11.7 and a Nd concentration ([Nd]) of 16 pmol/kg in the upper ~500 m of the eastern and central Fram Strait. Freshening and cooling of the AW on its way trough the AM are accompanied by a continuous change towards more radiogenic e-Nd signatures (e.g. -10.4 of dense Arctic Atlantic Water). This mainly reflects mixing with intermediate waters but also admixture of dense Kara Sea waters and Pacific-derived waters. The more radiogenic e-Nd signatures of the intermediate and deep waters (reaching -9.5) are mainly acquired in the SW Nordic Seas through exchange with basaltic formations of Iceland and CE Greenland. Inputs of Nd from Svalbard are not observed and surface waters and Nd on the Svalbard shelf originate from the Barents Sea. Shallow southward flowing Arctic-derived waters (〈200 m) form the core of the East Greenland Current above the Greenland slope and can be traced by their relatively radiogenic e-Nd (reaching -8.8) and elevated [Nd] (21-29 pmol/kg). These properties are used together with d18O and standard hydrographic tracers to define the proportions of Pacific-derived (〈~30% based on Nd isotopes) and Atlantic-derived waters, as well as of river waters (〈~8%). Shallow waters (〈150 m) on the NE Greenland Shelf share some characteristics of Arctic-derived waters, but exhibit less radiogenic epsilon-Nd values (reaching -12.4) and higher [Nd] (up to 38 pmol/kg) in the upper ~100 m. This suggests local addition of Greenland freshwater of up to ~6%. In addition to these observations, this study shows that the pronounced gradients in epsilon-Nd signatures and REE characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the AM.
    Keywords: GEOTRACES; Global marine biogeochemical cycles of trace elements and their isotopes
    Type: Dataset
    Format: application/zip, 4 datasets
    Location Call Number Limitation Availability
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    DATA PANGAEA
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