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  • 1
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    Short-term microbial and physico-chemical variability in low-temperature hydrothermal fluids near 5°S on the Mid-Atlantic Ridge (2009)
    Wiley
    In:  Environmental Microbiology, 11 (10). pp. 2526-2541.
    Details
    Publication Date: 2018-07-18
    Description: This study examines the representativeness of low-temperature hydrothermal fluid samples with respect to their chemical and microbiological characteristics. Within this scope, we investigated short-term temporal chemical and microbial variability of the hydrothermal fluids. For this purpose we collected three fluid samples consecutively from the same spot at the Clueless field near 5 degrees S on the southern Mid-Atlantic Ridge over a period of 50 min. During sampling, the temperature was monitored online. We measured fluid chemical parameters, characterized microbial community compositions and used statistical analyses to determine significant differences between the samples. Overall, the three fluid samples are more closely related to each other than to any other tested habitat. Therefore, on a broad scale, the three collected fluid samples can be regarded as habitat representatives. However, small differences are apparent between all samples. One of the Clueless samples even displayed significant differences (P-value 〈 0.01) to the other two Clueless samples. Our data suggest that the observed variations in fluid chemical and microbial compositions are not reflecting sampling artefacts but are related to short-term fluid variability due to dynamic subseafloor fluid mixing. Recorded temporal changes in fact reflect spatial heterogeneity found in the subsurface as the fluid flows through distinctive pathways. While conservative elements (Cl, Si, Na and K) indicate variable degrees of fluid-seawater mixing, reactive components, including Fe(II), O(2) and H(2)S, show that chemical and microbial reactions within the mixing zone further modify the emanating fluids on short-time scales. Fluids entrain microorganisms, which modify the chemical microenvironment within the subsurface biotopes. This is the first study focusing on short-term microbial variability linked to chemical changes in hydrothermal fluids.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1111/j.1462-2920.2009.01978.x
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral Sr/Ca records (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (3). pp. 846-857.
    Details
    Publication Date: 2019-02-01
    Description: The rising temperature of the world’s oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970–2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (〉338C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6 year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015GC006194
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Identification of a widespread Kamchatkan tephra: A middle Pleistocene tie-point between Arctic and Pacific paleoclimatic records (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 40 . pp. 3538-3543.
    Details
    Publication Date: 2017-05-24
    Description: Very few age controls exist for Quaternary deposits over the vast territory of the East Russian Arctic, which hampers dating of major environmental changes in this area and prevents their correlation to climatic changes in the Arctic and Pacific marine domains. We report a newly identified ~177 ka old Rauchua tephra, which has been dispersed over an area of 〉1,500,000 km2 and directly links terrestrial paleoenvironmental archives from Arctic Siberia with marine cores in the northwest Pacific, thus permitting their synchronization and dating. The Rauchua tephra can help to identify deposits formed in terrestrial and marine environments during the oxygen isotope stage 6.5 warming event. Chemical composition of volcanic glass from the Rauchua tephra points to its island-arc origin, while its spatial distribution singles out the Kamchatka volcanic arc as a source. The Rauchua tephra represents a previously unknown, large (magnitude 〉6.5) explosive eruption from the Kamchatka volcanic arc.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/grl.50645
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  • 4
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    Compositional variation and 226Ra-230Th model ages of axial lavas from the southern Mid-Atlantic Ridge, 8°48′S (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (1). pp. 199-218.
    Details
    Publication Date: 2019-09-23
    Description: We present geological observations and geochemical data for the youngest volcanic features on the slow-spreading Mid-Atlantic Ridge at 8°48'S that shows seismic evidence for a thickened crust and excess magma formation. Young lava flows with high sonar reflectivity cover about 14 km2 in the axial rift and were probably erupted from two axial volcanic ridges each of about 3 km in length. Three different lava units occur along an about 11 km long portion of the ridge, and lavas from the northern axial volcanic ridge differ from those of the southern axial volcanic ridge and surrounding lava flows. Basalts from the axial rift flanks and from a pillow mound within the young flows are more incompatible element depleted than those from the young volcanic field. Lavas from this volcanic area have 226Ra-230Th disequilibria model ages of 1,000 and 4,000 years whereas the older lavas from the rift flank and the pillow mound, but also some of the lava field, are older than 8,000 years. Glasses from the northern and southern ends of the southern lava unit indicate up to 100°C cooler magma temperatures than in the center and increased assimilation of hydrothermally altered material. The compositional heterogeneity on a scale of 3 km suggests small magma batches rising vertically from the mantle to the surface without significant lateral flow and mixing. The observations on the 8°48'S lava field support the model of low frequency eruptions from single ascending magma batches that has been developed for slow-spreading ridges.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015GC006016
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  • 5
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    High-resolution Sr/Ca ratios in a Porites lutea coral from Lakshadweep Archipelago, southeast Arabian Sea: An example from a region experiencing steady rise in the reef temperature (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 121 (1). pp. 252-266.
    Details
    Publication Date: 2019-09-23
    Description: Here we present the first record of Sr/Ca variability in a massive Porites lutea coral from the Lakshadweep Archipelago, Arabian Sea. The annual mean sea surface temperature (SST) in this region and the surrounding areas has increased steadily in the recent past. During some major El Nino events, SSTs are even higher, imposing additional thermal-stress on corals, episodically leading to coral bleaching. We infer from the coral-Sr/Ca record (1981-2008) that during some of these events high and persistent SSTs lead to a dampening of the temperature signal in coral-Sr/Ca, impairing the coral's ability to record full scale warming. Thus, coral-Sr/Ca may provide a history of past El Nino Southern-Oscillation (ENSO) induced thermal-stress episodes, which are a recurrent feature also seen in cross-spectral analysis between coral-Sr/Ca and the Nino3.4 index. Despite the impact of episodical thermal-stress during major El Nino events, our coral proxy faithfully records the seasonal monsoon-induced summer cooling on the order of approximate to 2.3 degrees C. Calibration of coral-Sr/Ca with instrumental grid-SST data shows significant correlation to regional SST and monsoon variability. Hence, massive Porites corals of this region are highly valuable archives for reconstructing long-term changes in SST, strongly influenced by monsoon variability on seasonal scales. More importantly, our data show that this site with increasing SST is an ideal location for testing the future effects of the projected anthropogenic SST increase on coral reefs that are already under thermal-stress worldwide.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015JC010821
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    New Insights into the mineralogy of the Atlantis II deep metalliferous sediments, Red Sea (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 16 (12). pp. 4449-4478.
    Details
    Publication Date: 2019-09-23
    Description: The Atlantis II Deep of the Red Sea hosts the largest known hydrothermal ore deposit on the ocean floor and the only modern analog of brine pool-type metal deposition. The deposit consists mainly of chemical-clastic sediments with input from basin-scale hydrothermal and detrital sources. A characteristic feature is the millimeter-scale layering of the sediments, which bears a strong resemblance to banded iron formation (BIF). Quantitative assessment of the mineralogy based on relogging of archived cores, detailed petrography, and sequential leaching experiments shows that Fe-(oxy)hydroxides, hydrothermal carbonates, sulfides, and authigenic clays are the main “ore” minerals. Mn-oxides were mainly deposited when the brine pool was more oxidized than it is today, but detailed logging shows that Fe-deposition and Mn-deposition also alternated at the scale of individual laminae, reflecting short-term fluctuations in the Lower Brine. Previous studies underestimated the importance of nonsulfide metal-bearing components, which formed by metal adsorption onto poorly crystalline Si-Fe-OOH particles. During diagenesis, the crystallinity of all phases increased, and the fine layering of the sediment was enhanced. Within a few meters of burial (corresponding to a few thousand years of deposition), biogenic (Ca)-carbonate was dissolved, manganosiderite formed, and metals originally in poorly crystalline phases or in pore water were incorporated into diagenetic sulfides, clays, and Fe-oxides. Permeable layers with abundant radiolarian tests were the focus for late-stage hydrothermal alteration and replacement, including deposition of amorphous silica and enrichment in elements such as Ba and Au.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015GC006010
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  • 7
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    Tracking interannual to multidecadal-scale climate variability in the Atlantic Warm Pool using central Caribbean coral data (2018)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-11-08
    Description: Atlantic Warm Pool (AWP) climate variability is subject to multiple influences of remote and local forcing. However, shortage of observational data before the mid‐20th century and of long‐term sea surface temperature (SST) and climate records has hampered the detection and investigation of decadal‐ and longer‐scale variability. We present new seasonally resolved 125‐year records of coral δ18O and Sr/Ca variations in the Central Caribbean Sea (Little Cayman, Cayman Islands; Diploria strigosa). Both geochemical proxies show decreasing long‐term trends, indicating long‐term warming. Sr/Ca indicates much stronger regional warming than large‐scale grid‐SST data, while δ18O tracks large‐scale SST changes in the AWP. Seawater δ18O variations are reconstructed, indicating a drying trend over the past century. High spatial correlation between coral δ18O and SST in the region of the Loop Current and Gulf Stream system suggests that Little Cayman is a sensitive location for detecting past large‐scale temperature variability beyond the central Caribbean region. More specifically, our δ18O data tracks changes in North Atlantic Oscillation (NAO) variability on decadal and multidecadal time scales providing insights into the temporal and spatial nonstationarity of the NAO. A combination of our δ18O record with two coral records from different Caribbean sites reveals high spatial correspondence between coral δ18O and SST variability in the North Atlantic subtropical gyre, where few instrumental measurements and proxies are available prior to the 20th century. Our results clearly demonstrate the potential of combining proxy data to provide information from sparsely sampled areas, helping to reduce uncertainty in model‐based projections.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Origin of isolated seamounts in the Canary Basin (East Atlantic): The role of plume material in the origin of seamounts not associated with hotspot tracks (2020)
    Wiley
    Details
    Publication Date: 2023-02-09
    Description: Despite their large number and in contrast to seamount chains, small solitary seamounts/seamount groups have rarely been sampled and therefore their origins remain enigmatic. Here we present 40Ar/39Ar, trace element and Nd‐Pb‐Hf isotope data from the solitary Demenitskoy Seamount, the isolated Tolkien seamount group and the Krylov Seamount and Ridge in the Canary Basin. Their chemical compositions range from intraplate ocean‐island‐basalt (Demenitskoy) to normal‐ and enriched‐mid‐ocean‐ridge‐basalt types (Tolkien and Krylov system, respectively). Lavas from all three seamount groups, however, show geochemical evidence for involvement of enriched (Canary/Cape Verde) plume material. Seismic tomography shows that large areas around these mantle plumes are affected by dispersal of presumably low‐velocity material, which also could have fed nearby isolated seamounts with diffusely‐upwelling plume material. This process may be extremely widespread but has been poorly studied to date.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    20th Century δ 18 O Seawater and Salinity Variations Reconstructed From Paired δ 18 O and Sr/Ca Measurements of a La Reunion Coral (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Paleoceanography and Paleoclimatology, 34 . pp. 2183-2200.
    Details
    Publication Date: 2022-01-31
    Description: Sea surface salinity (SSS) is an important variable in the global ocean circulation. However, decadal to interdecadal changes in SSS are not well understood due to the lack of instrumental data. Here we reconstruct SSS from a paired, bimonthly resolved coral δ18O and Sr/Ca record from La Reunion Island that extends from 1913 to 1995. Coral Sr/Ca correlates with regional sea surface temperature (SST) back to 1966, when instrumental coverage is good, while coral δ18O does not. The slope of the monthly (annual mean) coral Sr/Ca-SST regression is −0.040 mmol/mol per 1 °C (−0.068 mmol/mol per 1 °C) consistent with published estimates of the Sr/Ca-SST relationship. Coral Sr/Ca suggest a warming of 0.39 °C since 1913. δ18O seawater is calculated by subtracting the temperature component from measured coral δ18O, using coral Sr/Ca as well as historical SST products. The derived δ18O seawater reconstructions are correlated (r 〉 0.6), and all show a significant shift in the midtwentieth century (−0.17‰ to −0.19‰), indicating a freshening of SSS by 0.7 psu. However, the timing of this shift depends on the temperature component and varies from 1947 (δ18O seawater calculated with historical SST) to the late 1950s (δ18O seawater calculated with coral Sr/Ca). Coral Sr/Ca shows warm temperature anomalies in the mid-1950s, while historical SST products show warm anomalies from 1940 to 1945 followed by cooling in the 1950s, a pattern typical for the World War II bias. This suggests that historical SST may bias reconstructions of δ18O seawater and SSS from corals.
    Type: Article , PeerReviewed
    Format: text
    Format: other
    Format: text
    DOI: 10.1029/2019PA003770
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  • 10
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    Papanin Ridge and Ojin Rise Seamounts (Northwest Pacific): Dual Hotspot Tracks Formed by the Shatsky Plume (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Although previous findings support an origin of the Shatsky Rise igneous plateau (Northwest Pacific) through interaction of a mantle plume with a mid-ocean ridge triple junction, the evidence for the involvement of a mantle plume is equivocal. The identification of an intraplate hotspot track emanating from the plateau could solve this controversy. Here we present major and trace element geochemical data from two different bathymetric features that emanate from the youngest end of Shatsky Rise: Papanin Ridge and the Ojin Rise Seamount province. Combining our results with plate tectonic reconstructions, we conclude that Papanin Ridge represents a hotspot track formed by plume-ridge interaction. Whereas the southwestern part was formed along the path of the retreating Pacific-Farallon-Izanagi triple junction, the northeastern part was built by preferential drainage into its Pacific-Farallon branch. In contrast, the Ojin Rise Seamounts formed as a true intraplate hotspot track of the Shatsky plume tail. Our wide-ranging study reveals systematic spatial geochemical variations, consistent with a lithospheric thickness control on magma composition derived from melting a heterogeneous plume source. The recognition of two hotspot tracks and in particular of the Ojin Rise Seamounts as an intraplate hotspot track that is directly linked to Shatsky plateau volcanism both in terms of geochemistry and plate tectonic reconstructions confirms the long-disputed involvement of a mantle plume for the formation of Shatsky Rise.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: other
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