Alfred Wegener Institute for Polar and Marine Research
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The middle to Late Holocene environment on the Iturup Island (Kurils, North Western Pacific)
Get PDFThe Kuril Islands stretch southwest from Kamchatka, Russia, to Hokkaido, Japan and separate the Sea of Okhotsk from the northern Pacific Ocean. A series of transgressions and regressions linked to variations in climatically affected global ice volume are among the most important drivers of Holocene environmental changes in the region. Despite a long research history, reconstructions of the Holocene palaeoenvironment are sparse with inconsistent interpretations, arising from insufficient dating control, different temporal resolutions, and specific local geographical features, such as high tectonic activity and the isolated nature of the area. We have investigated a 550 cm lake sediment section from Iturup Island, the largest among the Kuril Islands. The 6600 year old sediment section was studied using sedimentological, geochemical, chironomid, diatom, and pollen analyses to reconstruct environmental and climatic changes and sea level fluctuations (transgression – regression stages). During the warm late phase of the Middle Holocene (6600–4400 cal BP) an open bay or lagoon with shallow overgrown littorals existed at the sampling site. The cooling between 5600 and 4400 cal BP can be correlated with Neoglacial cooling. The cool period between 4200 and 3200 cal BP was a transition towards the formation of a freshwater lagoon and can be related to a decline of the Japan Late Jomon transgression (Sakaguchi, 1983). Between 3200 and 2800 cal BP the lagoon separated from the marine environment in response to a further sea level decrease during the Japan Latest Jomon cold stage and regression. The following increase in the share of broad-leaved pollen indicated a slight warming (Yayoi transition stage) that was interrupted by a short-term cooling spell between 1500 and 1400 cal BP (cold Japan Kofun stage). The period between ca 1100 and 800 cal BP can be related to the European Medieval Climate Anomaly (MCA) or relatively dry Japan Nara-Heian-Kamakura warm stage. The Little Ice Age cooling and Edo regression were evident after ca 800 cal BP. Modern warming however is not well seen in the investigated core
The circumpolar impacts of climate change and anthropogenic stressors on Arctic cod (Boreogadus saida) and its ecosystem
Get PDFArctic cod (Boreogadus saida) is the most abundant forage fish in the Arctic Ocean. Here we review Arctic cod habitats, distribution, ecology, and physiology to assess how climate change and other anthropogenic stressors are affecting this key species. This review identifies vulnerabilities for different life stages across the entire distribution range of Arctic cod. We explore the impact of environmental (abiotic and biotic) and anthropogenic stressors on Arctic cod with a regional perspective in a scenario up to the year 2050 and identify knowledge gaps constraining predictions. Epipelagic eggs and larvae are more vulnerable to climate change and stressors than adults. Increased water temperatures, sea-ice decline, altered freshwater input, acidification, changing prey field, increased interspecific competition, new predators, and pollution are the principal stressors that will affect Arctic cod populations. Detrimental effects are likely to be greater in regions characterized by the advection of warmer Atlantic and Pacific waters. In contrast, Arctic cod may benefit from ocean warming in colder areas of the High Arctic. The risk from fisheries is moderate and primarily limited to bycatch. Overall, a decrease in suitable habitat and an associated decline in total Arctic cod biomass are predicted. In most Arctic seas, the relative abundance of Arctic cod within the fish community will likely fluctuate in accordance with cold and warm periods. A reduced abundance of Arctic cod will negatively affect the abundance, distribution, and physiological condition of certain predators, whereas some predators will successfully adapt to a more boreal diet. Regional management measures that recognize the critical role of Arctic cod are required to ensure that increased anthropogenic activities do not exacerbate the impacts of climate change on Arctic marine ecosystems. Ultimately, the mitigation of habitat loss for Arctic cod will only be achieved through a global reduction in carbon emissions
Precursor of disintegration of Greenland's largest floating ice tongue
Get PDFThe largest floating tongue of Greenland's ice sheet, Nioghalvfjerdsbræ, has been relatively stable with respect to areal retreat until 2022. Draining more than 6% of the ice sheet, a disintegration of Nioghalvfjerdsbræ's floating tongue and subsequent acceleration due to loss in buttressing are likely to lead to sea level rise. Therefore, the stability of the floating tongue is a focus of this study. We employed a suite of observational methods to detect recent changes at the calving front. We found that the calving style has changed since 2016 at the southern part of the eastern calving front, from tongue-type calving to a crack evolution initiated at frontal ice rises reaching 5-7km and progressing further upstream compared to 2010. The calving front area is further weakened by an area upstream of the main calving front that consists of open water and an ice mélange that has substantially expanded, leading to the formation of a narrow ice bridge. These geometric and mechanical changes may be a precursor of instability of the floating tongue. We complement our study by numerical ice flow simulations to estimate the impact of future ice-front retreat and complete ice shelf disintegration on the discharge of grounded ice. These idealized scenarios reveal that a loss of the south-eastern area of the ice shelf would lead to a 0.2% increase in ice discharge at the grounding line, while a sudden collapse of the frontal area (46% of the floating tongue area) will enhance the ice discharge by 5.1% due to loss in buttressing. Eventually, a full collapse of the floating tongue increases the grounding line flux by 166%
Different mechanisms of Arctic first-year sea-ice ridge consolidation observed during the MOSAiC expedition
Get PDFSea-ice ridges constitute a large fraction of the ice volume in the Arctic Ocean, yet we know little about the evolution of these ice masses. Here we examine the thermal and morphological evolution of an Arctic first-year sea-ice ridge, from its formation to advanced melt. Initially the mean keel depth was 5.6 m and mean sail height was 0.7 m. The initial rubble macroporosity (fraction of seawater filled voids) was estimated at 29% from ice drilling and 43%–46% from buoy temperature. From January until mid-April, the ridge consolidated slowly by heat loss to the atmosphere and the total consolidated layer growth during this phase was 0.7 m. From mid-April to mid-June, there was a sudden increase of ridge consolidation rate despite no increase in conductive heat flux. We surmise this change was related to decreased macroporosity due to transport of snow-slush to the ridge keel rubble via adjacent open leads. In this period, the mean thickness of the consolidated layer increased by 2.1 m. At the peak of melt in June–July we suggest that the consolidation was related to the refreezing of surface snow and ice meltwater and of ridge keel meltwater (the latter only about 15% of total consolidation). We used the morphology parameters of the ridge to calculate its hydrostatic equilibrium and obtained a more accurate estimate of the actual consolidation of the keel, correcting from 2.2 m to 2.8 m for average keel consolidation. This approach also allowed us to estimate that the average keel melt of 0.3 m, in June–July, was accompanied by a decrease in ridge draft of 0.9 m. An ice mass balance buoy in the ridge indicated total consolidation of 2.8 m, of which 2.1 m was related to the rapid mode of consolidation from April to June. By mid-June, consolidation resulted in a drastic decrease of the macroporosity of the interior of keel while the flanks had little or no change in macroporosity. These results are important to understanding the role of ridge keels as meltwater sources and sinks and as sanctuary for ice-associated organisms in Arctic pack ice
High-resolution simulation of the ocean circulation beneath the 79° North Glacier, Northeast Greenland
No full textPotential macroalgal expansion and blue carbon gains with northern Antarctic Peninsula glacial retreat
Get PDFThe West Antarctic Peninsula (WAP) is a hotspot of physical climate change, especially glacial retreat, particularly in its northern South Shetland Islands (SSI) region. Along coastlines, this process is opening up new ice-free areas, for colonization by a high biodiversity of flora and fauna. At Potter Cove, in the SSI (Isla 25 de Mayo/ King George Island), Antarctica, colonization by macroalgae was studied in two newly ice-free areas, a low glacier influence area (LGI), and a high glacier influence area (HGI) differing in the presence of sediment run-off and light penetration, which are driven by levels of glacial influence. We installed artificial substrates (tiles) at 5 m depth to analyze benthic algal colonization and succession for four years (2010–2014). Photosynthetic active radiation (PAR, 400–700 nm), temperature, salinity, and turbidity were monitored at both sites in spring and summer. The turbidity and the light attenuation (Kd) were significantly lower at LGI than at HGI. All tiles were colonized by benthic algae, differing in species identity and successional patterns between areas, and with a significantly higher richness at LGI than HGI in the last year of the experiment. We scaled up a quadrat survey on the natural substrate to estimate benthic algal colonization in newly deglaciated areas across Potter Cove. Warming in recent decades has exposed much new habitat, with macroalgae making up an important part of colonist communities ‘chasing’ such glacier retreat. Our estimation of algal colonization in newly ice-free areas shows an expansion of ~0.005–0.012 km2 with a carbon standing stock of ~0.2–0.4 C tons, per year. Life moving into new space in such emerging fjords has the potential to be key for new carbon sinks and export. In sustained climate change scenarios, we expect that the processes of colonization and expansion of benthic assemblages will continue and generate significant transformations in Antarctic coastal ecosystems by increasing primary production, providing new structures, food and refuge to fauna, and capturing and storing more Carbon
Vegetation Response to the Climate Change in Polar Chukotka from 2.510-2.554 Ma BP
Get PDFThe response of vegetation to climate change in Polar Chukotka between 2.510 and 2.554 Ma was determined by a palynological study of sediment cores from Lake Elgygytgyn recovered during the international expedition "El'gygytgyn Drilling Project". Six pollen zones were defined for this interval, which spans marine isotope stages (MIS) 101 and 100. Pollen zones 1 and 2 (MIS 101) as well as zones 3 and 4 (MIS 100) indicate the presence of Larix and Larix-Betula forests during interglaciations. The plant communities reflected in the spectra of zone 3 represent the warmest climates during the early Gelasian Age. During MIS 100, the period of maximum climate cooling is marked by the regional presence of shrub and herb dominated tundra (pollen zone 5). During the interstade (MIS 100, zone 6), the vegetation was dominated by Larix forest tundra. Pollen zones 3 and 4, which have spectra more indicative of interglacial rather than glacial plant communities, are more consistent with climate of MIS 101 and not MIS 100, as suggested by the core's age model. The incorrect age assignment of the boundary between these stages indicates that the Lake El'gygytgyn age model needs revision.</jats:p
A Model of Energy and Spectral Shape for the Internal Gravity Wave Field in the Deep Sea: The Parametric IDEMIX Model
Get PDFThe spectral description of the energy of oceanic internal gravity waves is generally represented by the Garrett–Munk (GM) model, a function with a power-law decrease of spectral energy in wavenumber–frequency space. Besides the slopes of these power laws, the spectrum is expressed as a function of energy and a bandwidth parameter that fixes the range of vertical modes excited in the respective state. Whereas concepts have been developed and agreed upon of what processes feed the wave spectrum and what dissipates energy, there is no explanation of what shapes the spectral distribution, i.e., how the power laws come about and what sets the bandwidth. The present study develops a parametric spectral model of energy and bandwidth from the basic underlying energy balance in terms of forcing, propagation, refraction, spectral transfer, and dissipation. The model is an extension of the IDEMIX (Internal Wave Dissipation, Energy and Mixing) models where bandwidth was taken as a constant parameter. The current version of the model is restricted to single-column mode and the slopes of the spectral power laws are fixed. A coupled system of predictive equations for energy and bandwidth (for up- and downward propagating waves) results. The equations imply that bandwidth relates to energy by a power law with an exponent given by the dynamical parameters. It agrees favorably with energy, bandwidth, and slope data from previously published fits of the GM model to Argo float observations. Numerical solutions of the coupled energy–bandwidth model in stand-alone modus are presented