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  • 1
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    Online Resource
    Impact of a long-lived anticyclonic mesoscale eddy on seawater anomalies in the northeastern tropical Pacific Ocean: a composite analysis from hydrographic measurements, sea level altimetry data, and reanalysis model products
    Copernicus GmbH ; 2022
    In:  Ocean Science Vol. 18, No. 4 ( 2022-08-08), p. 1163-1181
    Details
    In: Ocean Science, Copernicus GmbH, Vol. 18, No. 4 ( 2022-08-08), p. 1163-1181
    Abstract: Abstract. Using observational data, satellite altimeters, and reanalysis model products, we have investigated eddy-induced seawater anomalies and heat and salt transport in the northeastern tropical Pacific Ocean. An eddy detection algorithm (EDA) was used to identify eddy formation at the Mexican Tehuantepec Gulf (TT) in July 2018 during an unusually strong summer wind event. The eddy separated from the coast with a mean translation velocity of 11 cm s−1 and a mean radius of 115 km and traveled 2050–2400 km westwards off the Central American coast, where it was followed at approx 114∘ W and 11∘ N for oceanographic observation between April and May 2019. The in situ observations show that the major eddy impacts are restricted to the upper 300 m of the water column and are traceable down to 1500 m water depth. In the eddy core at 92 m water depth an extreme positive temperature anomaly of 8.2 ∘C, a negative salinity anomaly of −0.78 psu, a positive fluorescence anomaly of +0.8 mg m−3, and a positive dissolved oxygen concentration anomaly of 137 µmol kg−1 are observed. Compared with annual climatological averages in 2018, the water trapped within the eddy is estimated to transport an average positive westward zonal heat anomaly of 85×1012 W and an average westward negative salt anomaly of -2.1×106 kg s−1. The heat transport is the equivalent of 1 % of the total annual zonal eddy-induced heat transport at this latitude in the Pacific Ocean. Understanding the dynamics of long-lived mesoscale eddies that may reach the seafloor in this region of the Pacific Ocean is especially important in light of potential deep-sea mining activities that are being targeted on this area.
    Type of Medium: Online Resource
    ISSN: 1812-0792
    URL: Article
    URL: Article
    DOI: 10.5194/os-18-1163-2022
    DOI: 10.5194/os-18-1163-2022-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
    detail.hit.zdb_id: 2183769-7
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  • 2
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    Evidence of eddy-related deep-ocean current variability in the northeast tropical Pacific Ocean induced by remote gap winds
    Copernicus GmbH ; 2020
    In:  Biogeosciences Vol. 17, No. 24 ( 2020-12-23), p. 6527-6544
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 17, No. 24 ( 2020-12-23), p. 6527-6544
    Abstract: Abstract. There has been a steady increase in interest in mining of deep-sea minerals in the Clarion–Clipperton Zone (CCZ) in the eastern Pacific Ocean during the last decade. This region is known to be one of the most eddy-rich regions in the world ocean. Typically, mesoscale eddies are generated by intense wind bursts channeled through gaps in the Sierra Madre mountains in Central America. Here, we use a combination of satellite and in situ observations to evaluate the relationship between deep-sea current variability in the region of potential future mining and eddy kinetic energy (EKE) in the vicinity of gap winds. A geometry-based eddy detection algorithm has been applied to altimetry sea surface height data for a period of 24 years, from 1993 to 2016, in order to analyze the main characteristic parameters and the spatiotemporal variability of mesoscale eddies in the northeast tropical Pacific Ocean (NETP). Significant differences between the characteristics of eddies with different polarity (cyclonic vs. anticyclonic) were found. For eddies with lifetimes longer than 1 d, cyclonic polarity is more common than anticyclonic rotation. However, anticyclonic eddies are larger in size, show stronger vorticity, and survive longer in the ocean than cyclonic eddies (often 90 d or more). Besides the polarity of eddies, the location of eddy formation should be taken into consideration when investigating the impacted deep-ocean region as we found eddies originating from the Tehuantepec (TT) gap winds lasting longer in the ocean and traveling farther distances in a different direction compared to eddies produced by the Papagayo (PP) gap winds. Long-lived anticyclonic eddies generated by the TT gap winds are observed to travel distances up to 4500 km offshore, i.e., as far as west of 110∘ W. EKE anomalies observed in the surface of the central ocean at distances of ca. 2500 km from the coast correlate with the seasonal variability of EKE in the region of the TT gap winds with a time lag of 5–6 months. A significant seasonal variability of deep-ocean current velocities at water depths of 4100 m was observed in multiple-year time series data, likely reflecting the energy transfer of the surface EKE generated by the gap winds to the deep ocean. Furthermore, the influence of mesoscale eddies on deep-ocean currents is examined by analyzing the deep-ocean current measurements when an anticyclonic eddy crosses the study region. Our findings suggest that despite the significant modulation of dominant current directions driven by the bottom-reaching eddy, the current magnitude intensification was not strong enough to trigger local sediment resuspension in this region. A better insight into the annual variability of ocean surface mesoscale activity in the CCZ and its effects on deep-ocean current variability can be of great help to mitigate the impact of future potential deep-sea mining activities on the benthic ecosystem. On an interannual scale, a significant relationship between cyclonic eddy characteristics and El Niño–Southern Oscillation (ENSO) was found, whereas a weaker correlation was detected for anticyclonic eddies.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    DOI: 10.5194/bg-17-6527-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2158181-2
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  • 3
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    Small-scale heterogeneity of trace metals including rare earth elements and yttrium in deep-sea sediments and porewaters of the Peru Basin, southeastern equatorial Pacific
    Copernicus GmbH ; 2019
    In:  Biogeosciences Vol. 16, No. 24 ( 2019-12-20), p. 4829-4849
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 16, No. 24 ( 2019-12-20), p. 4829-4849
    Abstract: Abstract. Due to its remoteness, the deep-sea floor remains an understudied ecosystem of our planet. The patchiness of existing data sets makes it difficult to draw conclusions about processes that apply to a wider area. In our study we show how different settings and processes determine sediment heterogeneity on small spatial scales. We sampled solid phase and porewater from the upper 10 m of an approximately 7.4×13 km2 area in the Peru Basin, in the southeastern equatorial Pacific Ocean, at 4100 m water depth. Samples were analyzed for trace metals, including rare earth elements and yttrium (REY), as well as for particulate organic carbon (POC), CaCO3, and nitrate. The analyses revealed the surprisingly high spatial small-scale heterogeneity of the deep-sea sediment composition. While some cores have the typical green layer from Fe(II) in the clay minerals, this layer is missing in other cores, i.e., showing a tan color associated with more Fe(III) in the clay minerals. This is due to varying organic carbon contents: nitrate is depleted at 2–3 m depth in cores with higher total organic carbon contents but is present throughout cores with lower POC contents, thus inhibiting the Fe(III)-to-Fe(II) reduction pathway in organic matter degradation. REY show shale-normalized (SN) patterns similar to seawater, with a relative enrichment of heavy REY over light REY, positive LaSN anomaly, negative CeSN anomaly, and positive YSN anomaly and correlate with the Fe-rich clay layer and, in some cores, also correlate with P. We therefore propose that Fe-rich clay minerals, such as nontronite, as well as phosphates, are the REY-controlling phases in these sediments. Variability is also seen in dissolved Mn and Co concentrations between sites and within cores, which might be due to dissolving nodules in the suboxic sediment, as well as in concentration peaks of U, Mo, As, V, and Cu in two cores, which might be related to deposition of different material at lower-lying areas or precipitation due to shifting redox boundaries.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    URL: Article
    DOI: 10.5194/bg-16-4829-2019
    DOI: 10.5194/bg-16-4829-2019-supplement
    DOI: 10.5194/bg-16-4829-2019-corrigendum
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2158181-2
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  • 4
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    Assessing the temporal scale of deep-sea mining impacts on sediment biogeochemistry
    Copernicus GmbH ; 2020
    In:  Biogeosciences Vol. 17, No. 10 ( 2020-05-26), p. 2767-2789
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 17, No. 10 ( 2020-05-26), p. 2767-2789
    Abstract: Abstract. Deep-sea mining for polymetallic nodules is expected to have severe environmental impacts because not only nodules but also benthic fauna and the upper reactive sediment layer are removed through the mining operation and blanketed by resettling material from the suspended sediment plume. This study aims to provide a holistic assessment of the biogeochemical recovery after a disturbance event by applying prognostic simulations based on an updated diagenetic background model and validated against novel data on microbiological processes. It was found that the recovery strongly depends on the impact type; complete removal of the reactive surface sediment reduces benthic release of nutrients over centuries, while geochemical processes after resuspension and mixing of the surface sediment are near the pre-impact state 1 year after the disturbance. Furthermore, the geochemical impact in the DISturbance and reCOLonization (DISCOL) experiment area would be mitigated to some degree by a clay-bound Fe(II)-reaction layer, impeding the downward diffusion of oxygen, thus stabilizing the redox zonation of the sediment during transient post-impact recovery. The interdisciplinary (geochemical, numerical and biological) approach highlights the closely linked nature of benthic ecosystem functions, e.g. through bioturbation, microbial biomass and nutrient fluxes, which is also of great importance for the system recovery. It is, however, important to note that the nodule ecosystem may never recover to the pre-impact state without the essential hard substrate and will instead be dominated by different faunal communities, functions and services.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    DOI: 10.5194/bg-17-2767-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2158181-2
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  • 5
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    Impact of small-scale disturbances on geochemical conditions, biogeochemical processes and element fluxes in surface sediments of the eastern Clarion–Clipperton Zone, Pacific Ocean
    Copernicus GmbH ; 2020
    In:  Biogeosciences Vol. 17, No. 4 ( 2020-02-28), p. 1113-1131
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 17, No. 4 ( 2020-02-28), p. 1113-1131
    Abstract: Abstract. The thriving interest in harvesting deep-sea mineral resources, such as polymetallic nodules, calls for environmental impact studies and, ultimately, for regulations for environmental protection. Industrial-scale deep-sea mining of polymetallic nodules most likely has severe consequences for the natural environment. However, the effects of mining activities on deep-sea ecosystems, sediment geochemistry and element fluxes are still poorly understood. Predicting the environmental impact is challenging due to the scarcity of environmental baseline studies as well as the lack of mining trials with industrial mining equipment in the deep sea. Thus, currently we have to rely on small-scale disturbances simulating deep-sea mining activities as a first-order approximation to study the expected impacts on the abyssal environment. Here, we investigate surface sediments in disturbance tracks of seven small-scale benthic impact experiments, which have been performed in four European contract areas for the exploration of polymetallic nodules in the Clarion–Clipperton Zone (CCZ) in the NE Pacific. These small-scale disturbance experiments were performed 1 d to 37 years prior to our sampling program in the German, Polish, Belgian and French contract areas using different disturbance devices. We show that the depth distribution of solid-phase Mn in the upper 20 cm of the sediments in the CCZ provides a reliable tool for the determination of the disturbance depth, which has been proposed in a previous study from the SE Pacific (Paul et al., 2018). We found that the upper 5–15 cm of the sediments was removed during various small-scale disturbance experiments in the different exploration contract areas. Transient transport-reaction modeling for the Polish and German contract areas reveals that the removal of the surface sediments is associated with the loss of the reactive labile total organic carbon (TOC) fraction. As a result, oxygen consumption rates decrease significantly after the removal of the surface sediments, and, consequently, oxygen penetrates up to 10-fold deeper into the sediments, inhibiting denitrification and Mn(IV) reduction. Our model results show that the return to steady-state geochemical conditions after the disturbance is controlled by diffusion until the reactive labile TOC fraction in the surface sediments is partly re-established and the biogeochemical processes commence. While the re-establishment of bioturbation is essential, steady-state geochemical conditions are ultimately controlled by the delivery rate of organic matter to the seafloor. Hence, under current depositional conditions, new steady-state geochemical conditions in the sediments of the CCZ are reached only on a millennium scale even for these small-scale disturbances simulating deep-sea mining activities.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-17-1113-2020
    DOI: 10.5194/bg-17-1113-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2158181-2
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