Alfred Wegener Institute for Polar and Marine Research
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Biophysical characterization of summer Arctic sea-ice habitats using a remotely operated vehicle-mounted underwater hyperspectral imager
Get PDFThe impact of a rapidly shifting sea-ice cover on climate, ecosystem processes and biophysical habitat properties is not yet fully understood, particularly in the central Arctic Ocean, due to a lack of spatially representative observations. From June to July 2020 during the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC, leg 4) in the Transpolar Drift, we deployed an underwater hyperspectral imager (UHI) mounted on a remotely operated vehicle (ROV) to characterize the biophysical properties of different sea-ice habitats. We conducted UHI surveys along two transects: i) under level first-year sea ice (FYI), which had a mean sea-ice draft of 1.4 m and was composed of primarily level FYI but also had a relatively shallow ridge (keel depth ∼2.6 m); and ii) under the flank of a ridge, named Jaridge, with a mean ice draft of 1.7 m, which was composed of a mix of level ice and thicker ridge blocks with over 3 m draft. We present a new unsupervised bio-optical quantification algorithm for hyperspectral surveys, the relative ice algal biomass index (RBI), using spectral mixture analysis (SMA). We compare this method to the supervised machine learning habitat classification algorithm, Support Vector Machine (SVM). The RBI showed good agreement to literature-based normalized difference indices (NDI) and PCA analyses, which confirm the RBI as a reliable unsupervised index for ice algal biomass. Our biophysical characterization of the two surveyed regions showed an association of sea-ice algal biomass with sea-ice ridge features. Our surveys also indicate that ice algal spatial distribution may be influenced by ice melt rates, and the formation of under ice meltwater layers and false bottoms. With high spatial coverage (>100 m) at microscale resolution (∼cm) we documented large spatial variability of summer Arctic sea-ice algal biomass and different patterns between adjacent ice habitats. We further demonstrate the need for improved understanding of sea-ice algal spatial variability as a complementary tool for sea-ice biogeochemical sampling using destructive ice core sampling
Corrigendum: Spatiotemporal evolution of melt ponds on Arctic sea ice: MOSAiC observations and model results
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A benthic mesocosm system for long‐term multi‐factorial experiments applying predicted warming and realistic microplastic pollution scenarios
No full textAbstractPredicting anthropogenic impacts on benthic marine ecosystems is of great importance for conservation. Climate change models have indicated that increasing seawater temperatures will drive shifts in the distribution of benthic organisms due to species‐specific thermal tolerances. When combined with other stressors such as pollutants, interactive effects may lead to even greater impacts. Microplastics (MP), as a marine pollutant, have been shown to elicit responses in organisms but often at concentrations far greater than experienced in the environment and with short‐term exposure times. Assessing long‐term interactive effects of MP pollution and ocean warming on benthic marine organisms has not been previously addressed. A unique mesocosm facility was constructed on the island of Helgoland, in the southern North Sea, to explore the combined impacts of these two factors. The multi‐factorial experimental system is composed of 16 independent benthic mesocosms, utilizing novel features and methods for the continuous generation of climate change and MP exposure scenarios, while retaining natural conditions for other environmental parameters. We provide a description of the system design and methods, followed by an operational performance assessment during a 10‐month exposure experiment with European flat oysters (Ostrea edulis), evaluated on the accuracy of exposure scenario control and the degree of realism achieved. We demonstrate the novel application of kinetic modeling for generating environmentally relevant MP exposure conditions (+ 25 MP L−1), and highlight the mesocosm systems suitability for studying chronic effects of MP pollution and ocean warming on benthic marine ecosystems through its real‐world application.</jats:p
The Pauzhetka tephra (South Kamchatka): A key middle Pleistocene isochron for the Northwest Pacific and Okhotsk Sea sediments
No full textThe distal Pauzhetka tephra, formed by a large caldera-forming volcanic eruption in South Kamchatka, has been identified in eleven recently recovered marine sediment cores based on major and trace element compositions of tephra glass. Ten SO264 cores form a transect along the Emperor Seamount Chain (ESC) in the Northwest (NW) Pacific between ∼50.3° and ∼45°N, 800–1200 km southeast of the Pauzhetka caldera. One additional core LV28-41-4 was retrieved in the Okhotsk Sea, ∼600 km west of the caldera. The Pauzhetka tephra glass shards have a characteristic medium-K rhyolite composition and trace element content compatible with the rear-arc position of the source volcano that ensures their identification. In the NW Pacific SO264 cores, the tephra is preserved as layers in cores 33, 47, 49, 53, 55, 56 and 62, as a lens in core 45, and as cryptotephra in cores 57 and 66. It forms a cryptotephra in the Okhotsk Sea core LV28-41-4. Distinctively high XRF-retrieved K/Ti and K/Fe ratios compared to those for the host sediments help identify the Pauzhetka tephra. According to our refined stable oxygen isotope (δ18O)- and magneto-stratigraphy of two studied and two reference cores, the Pauzhetka tephra occurs within a local δ18O maximum during a transition from marine isotope stage 12 to 11c (Termination V) and below a paleointensity minimum referred to as the Bermuda excursion, at ca. 418 ka. Using the tephra age as an isochron, we show that average linear sedimentation rates decrease southward along a transect of the SO264 cores, except in core 55. It partially reflects an intensification of mid-depth currents causing winnowing, erosion or non-deposition along the ESC over the past 418 kyr. An increased linear sedimentation rate in core 55, recovered from the southern leeward side of the Minnetonka Seamount, appears to record the pelagic accumulation protected from the mid-depth current influence. Our findings expand the former ash dispersal area farther southeast in the NW Pacific and southwest in the Okhotsk Sea. The new data on the tephra thickness supports the axis direction of the fallout zone southeast of the Pauzhetka caldera. Our results suggest the Pauzhetka tephra as a key middle Pleistocene isochron for the stratigraphy and correlation of the NW Pacific and Okhotsk Sea sediments
Earth Virtualization Engines (EVE)
Get PDFTo manage Earth in the Anthropocene, new tools, new institutions, and new forms of international cooperation will be required. Earth Virtualization Engines is proposed as an international federation of centers of excellence to empower all people to respond to the immense and urgent challenges posed by climate change
Exploring the ocean mesoscale at reduced computational cost with FESOM 2.5: efficient modeling strategies applied to the Southern Ocean
Get PDFModeled projections of climate change typically do not include a well-resolved ocean mesoscale due to the high computational cost of running high-resolution models for long time periods. This challenge is addressed using efficiency-maximizing modeling strategies applied to 3km simulations of the Southern Ocean in past, present, and future climates. The model setup exploits reduced-resolution spin-up and transient simulations to initialize a regionally refined, high-resolution ocean model during short time periods. The results are compared with satellite altimetry data and more traditional eddy-present simulations and evaluated based on their ability to reproduce observed mesoscale activity and to reveal a response to climate change distinct from natural variability. The high-resolution simulations reproduce the observed magnitude of Southern Ocean eddy kinetic energy (EKE) well, but differences remain in local magnitudes and the distribution of EKE. The coarser, eddy-permitting ensemble simulates a similar pattern of EKE but underrepresents observed levels by 55%. At approximately 1° C of warming, the high-resolution simulations produce no change in overall EKE, in contrast to full ensemble agreement regarding EKE rise within the eddy-permitting simulations. At approximately 4° C of warming, both datasets produce consistent levels of EKE rise in relative terms, although not absolute magnitudes, as well as an increase in EKE variability. Simulated EKE rise is concentrated where flow interacts with bathymetric features in regions already known to be eddy-rich. Regional EKE change in the high-resolution simulations is consistent with changes seen in at least four of five eddy-permitting ensemble members at 1° C of warming and all ensemble members at 4° C. However, substantial noise would make these changes difficult to distinguish from natural variability without an ensemble
Monitoring aerosol optical depth during the Arctic night: Instrument development and first results
Get PDFMoon-photometric measurements were made at two locations in the Arctic during winter nights using two different modified Sun photometers; a Carter Scott SP02 and a Precision Filter Radiometer (PFR) developed at PMOD/WRC. Values of aerosol optical depth (AOD) were derived from spectral irradiance measurements made at four wavelengths for each of the devices. The SP02 was located near Barrow, Alaska and recorded data from November 2012 to March 2013, spanning five lunar cycles, while the PFR was deployed to Ny-Ålesund, Svalbard each winter from February 2014 to February 2019 for a total of 56 measurement periods. A methodology was developed to process the raw data, involving calibration of the instruments and normalizing measured spectral irradiance values in accordance with site-specific determinations of the extraterrestrial atmospheric irradiance (ETI) as Moon phase cycled. Uncertainties of the derived AOD values were also evaluated and found to be in the range, 0.006–0.030, depending on wavelength and which device was evaluated. The magnitudes of AOD determined for the two sites were in general agreement with those reported in the literature for sunlit periods just before and after the dark periods of Arctic night. Those for the PFR were also compared with data obtained using star photometers and a Cimel CE318-T, recently deployed to Ny-Ålesund, showing that Moon photometry is viable as a means to monitor AOD during the Arctic night. Such data are valuable for more complete assessments of the role aerosols play in modulating climate, the validation of AOD derived using various remote sensing techniques, and applications related to climate modeling
EVOLUTION OF GROUNDING-LINE RETREAT ALONG THE MAC. ROBERTSON SHELF (EAST ANTARCTICA) FOR THE PAST 30,000 YEARS: CREATING RELIABLE SPATIOTEMPORAL BENCHMARKS FOR VALIDATING ICE-SHEET SIMULATIONS
No full textThe future behaviour of the Antarctic Ice Sheet is considered as one of the largest unknowns in global climate predictions. Dramatic and accelerating ice loss has been observed over the past few decades for numerous drainage basins of the ice sheet (Bentley et al., 2014, Mackintosh et al., 2014). However, those records only reflect a short moment of limited informative value when considering the length of a full cycle of ice sheet build-up and retreat. This emphasizes the strong need for reliable long-term data of ice-sheet change in time and space, particularly for sectors along the East Antarctic margin that play key roles in supplying the world oceans with bottom waters (Ohshima et al., 2013). We present newly acquired geophysical and geological datasets from the previously poorly studied east Antarctic Mac. Robertson Shelf (Leventer et al. 2006, Mackintosh et al., 2011). Combined analyses of these data will allow for creating a four-dimensional framework of ice-sheet change over the past ~30,000 years. These unique data provide valuable spatiotemporal records for benchmarking paleo-ice sheet models and thus contribute to improve simulations of ice-sheet changes in the coming decades and centuries. Furthermore, they advance our understanding of past variability in the formation of Antarctic Bottom Water that originates in this region today