Alfred Wegener Institute for Polar and Marine Research
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Functional diversity loss and taxonomic delays of European freshwater fish and North American breeding birds
Get PDFBiodiversity is temporally dynamic, reflecting historical environmental conditions and influencing ecosystem stability. Colonisation and extinction dynamics frequently exhibit asynchronous patterns, resulting in net imbalances and thus to long-lasting richness trends. If these trends are not functionally random, functional net imbalances between colonisations and extinctions (fNICE) are likely to emerge. Using community time series data of European freshwater fish and North American breeding birds, we investigated how fNICE differs from its taxonomic equivalent (tNICE), to provide a comprehensive picture of biodiversity dynamics. Our findings reveal that taxonomic and functional delays are a prevalent feature, challenging the assumption of an immediate response to environmental changes. Taxonomic delays manifest as extinction debts and colonisation credits, while functional delays indicate a shift in the balance between functional gains and losses over time. Moreover, we found that taxonomic and functional imbalances are not always directly correlated, although some specific patterns were found consistently for fish and birds. Early colonisations outpaced functional gains, indicating that although new species arrived earlier than the extinction of other species, the acquisition of new functional traits lagged. Although this may temporarily stabilise communities, as functional redundancy can mitigate loss of function via local extinctions, excessive redundancy can compromise biodiversity's capacity to respond to environmental variations, thereby undermining long-term resilience. In conclusion, understanding the intricate temporal dynamics of biodiversity responses is paramount for effective conservation practices. While short-term observations may suggest an equilibrium between diversity and the environmental conditions, our results underscore the importance of considering long-term dynamics and the interplay between species traits and changing environments. The metrics tNICE and fNICE are valuable tools for quantifying these temporal dynamics and unravelling their consequences for ecosystem stability. Incorporating these insights into conservation strategies can aid in proactively preserving biodiversity and safeguarding the integrity of ecosystems. Read the free Plain Language Summary for this article on the Journal blog
Atmosphere circulation patterns synchronize pan-Arctic glacier melt and permafrost thaw
Get PDFThe Arctic is changing rapidly due to the amplification of global temperature trends, causing profound impacts on the ice sheet in Greenland, glaciers, frozen ground, ecosystems, and societies. Here, we focus on impacts that atmospheric circulation causes in addition to the climate warming trends. We combine time series of glacier mass balance from temporal satellite gravimetry measurements (GRACE/GRACE-FO; 2002–2023), active layer thickness in permafrost areas from ESA’s Climate Change Initiative remote sensing and modelling product (2003–2019), and field measurements of the Circumpolar Active Layer Monitoring Network (2002–2023). Despite regional and system-related complexities, we identify robust covariations between these observations, which vary asynchronously between neighbouring regions and synchronously in regions antipodal to the North Pole. We reveal a close connection with dominant modes of atmosphere circulation, controlling about 75% of the common pan-Arctic impact variability (2002–2022), also affecting the Greenland Ice Sheet. We emphasize that it is necessary to consider such atmospheric driving patterns when projecting impacts, particularly caused by extremes, in an increasingly warmer Arctic
Restoration of European oyster (Ostrea edulis) in the German North Sea (RESTORE preliminary investigation)
Get PDFAs hotspots of biodiversity, oyster reefs fulfil important ecological functions. Being biogenic
reef builders, for many animal species they provide food, a substrate for colonisation, and a
space to spawn and find shelter, thus increasing biodiversity. By filtering the water they im
prove water quality and enhance benthic-pelagic coupling.
European oyster (Ostrea edulis) and the oyster banks they form were once widespread in the
North Sea. Due to overfishing until the 1920s, the species is considered functionally extinct in
the German Bight. The testing and development project RESTORE, supported by the BfN with
BMUV funding, is investigating methods for the restoration of the European oyster population
in the German North Sea. For the purpose of sustainable population development, the project
is working on technological and biological challenges and aspects of nature conservation law,
and develops and trials methods for practical implementation as a part of marine nature con
servation measures.
The preliminary investigation provided the legal framework for the practical testing of
measures to restore European oyster in the Borkum Reef Ground Nature Conservation Area
(NCA). It helped to establish a comprehensive knowledge and technology transfer network in
Europe. RESTORE initiated the creation of the Native Oyster Restoration Alliance (NORA),
where European projects for the restoration of the native oyster work closely together. Com
prehensive field studies conducted during the preliminary investigation confirmed the funda
mental suitability of European oyster for restoration in the German North Sea under the en
vironmental conditions that prevail today. The preliminary investigation identified the specific
challenge of availability of suitable seed oysters for marine conservation measures and devel
oped suggestions for solutions. RESTORE recommended the establishment of a German seed
oyster breeding programme for long-term restoration measures. This is now being imple
mented funded by the Federal Biodiversity Programme within the context of the PROCEED
project. Through extensive laboratory and field experiments, the preliminary investigation
identified suitable substrates that can be used in oyster breeding and in the practical imple
mentation of restoration measures in the field.
In conclusion, the preliminary investigation recommended the construction and scientific in
vestigation of a pilot oyster reef in the Borkum Reef Ground NCA. All legal, biological and tech
nological requirements have been identified, so that this next step can be carried out as part
of the RESTORE main project and subsequently evaluated by scientific monitoring
Glacial history of the King Haakon Trough System, sub-Antarctic South Georgia
No full textIn an effort to elucidate an important part of the Quaternary evolution of sub-Antarctic South Georgia, hydroacoustic data from its southern continental shelf are presented. The island with its surrounding shelf is of key interest for climate reconstructions, because it is located within the core belt of the Southern Westerlies and between the main fronts of the Antarctic Circumpolar Current in the Southern Ocean. This makes it particularly susceptible to changes in climate conditions on a local, regional, but also Southern Hemisphere-wide scale.
The data provide new insights into the glacial evolution of the King Haakon Trough, one of several cross-shelf trough systems around the island. Numerous landforms, identified from high-resolution bathymetry data, document phases of ice advance and retreat. They are interpreted to be related to the confluence of two major trunk glaciers fed by an extended, possibly warm-based, South Georgia Ice Cap. Linear bedforms become progressively elongated towards the shelf and imply accelerated ice flow and/or softer sediment substrate towards the shelf edge. In contrast, recessional moraines and large morainal banks not only evidence shelf-wide ice extent during a peak glaciation, but also attest to staggered retreat, at least during the initial phase of deglaciation. The establishment of a complex bottom-current system around the onset of the last deglaciation is implied by the presence of moats and contourite drifts, which are mainly recorded in sub-bottom profiler data from the trough system. These data also show an acoustically semi-transparent facies of variable thickness present on the mid- and outer shelf as basal trough fill, which, on the basis of its acoustic appearance and the presence of several strong internal reflectors, is interpreted as a sequence of stacked glacial tills. These are similar to stacked tills previously documented from the Antarctic Peninsula and probably document a minimum of three extensive ice advances around South Georgia. Because the tills in the King Haakon Trough occur over a distance of ~26 km across the shelf, it is postulated that they derive from a minimum of three separate glaciations, rather than from re-advances within one glaciation period. Accordingly, the new findings from the combined bathymetry and sub-bottom profiler data show that the marine-geological archives around South Georgia offer unique potential to constrain how ice masses in the Southern Ocean responded to Quaternary climate change.</jats:p
Spatial and temporal variability in Holocene trough-fill sediments, King Haakon Trough System, sub-Antarctic South Georgia
Get PDFThe climate in the South Atlantic sector of the sub-Antarctic, and therefore on and around the island of South Georgia, is dependent on the Southern Hemisphere Westerlies (SHW) and the Antarctic Circumpolar Current (ACC). The SHW and the ACC, in turn, are strongly controlled by climate variability in the Southern Hemisphere. Accordingly, thick sediment sequences in the troughs across South Georgia's continental shelf serve as valuable archives for past climate variations in the Southern Ocean. Since Holocene climate fluctuations led to only minimal oscillations in glacier margin positions within the fjords, the entire shelf was exposed to dynamic ocean currents since at least 10 ka BP. Its depositional systems are therefore a suitable target for the reconstruction of Holocene dynamics of both the SHW and the ACC. Sub-bottom profiler data and radiocarbon ages from four gravity cores from the south-western South Georgia continental shelf provide evidence for a complex interplay between island run-off and ocean currents intruding into a unique cross-shelf trough system during the last ∼10 ka. The data reveal several prominent changes in sediment and Holocene climate dynamics, the most significant occurring between 8 and 7.7 cal ka BP and between 2.6 and 2.2 cal ka BP. Both of these time periods represent transitions from warmer to cooler and windier conditions in South Georgia and the Southern Hemisphere. Our record from the King Haakon Trough System is the first highly resolved Holocene archive from the marine realm on the south-western South Georgia continental shelf and suggests several large-scale Southern Hemisphere climate changes during the mid-to late Holocene
The EnMAP spaceborne imaging spectroscopy mission: Initial scientific results two years after launch
Get PDFRecords reveal the vast historical extent of European oyster reef ecosystems
Get PDFAnthropogenic activities have impacted marine ecosystems at extraordinary scales. Biogenic reef ecosystems built by the European flat oyster (Ostrea edulis) typically declined before scientific monitoring. The past form and extent of these habitats thus remains unknown, with such information potentially providing valuable perspectives for current management and policy. Collating >1,600 records published over 350 years, we created a map of historical oyster reef presence at the resolution of 10 km2 across its biogeographic range, including documenting abundant reef habitats along the coasts of France, Denmark, Ireland and the United Kingdom. Spatial extent data were available from just 26% of locations yet totalled >1.7 million hectares (median reef size = 29.9 ha, range 0.01–1,536,000 ha), with 190 associated macrofauna species from 13 phyla described. Our analysis demonstrates that oyster reefs were once a dominant three-dimensional feature of European coastlines, with their loss pointing to a fundamental restructuring and ‘flattening’ of coastal and shallow-shelf seafloors. This unique empirical record demonstrates the highly degraded nature of European seas and provides key baseline context for international restoration commitments
Sea ice melt pond bathymetry reconstructed from aerial photographs using photogrammetry: a new method applied to MOSAiC data
Get PDFMelt ponds are a core component of the summer sea ice system in the Arctic, increasing the uptake of solar energy and impacting the ice-associated ecosystem. They were thus one of the key topics during the 1-year drift campaign Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) in the Transpolar Drift 2019/2020. Pond depth is a dominating factor in describing the surface meltwater volume; it is necessary to estimate budgets and used in model parameterization to simulate pond coverage evolution. However, observational data on pond depth are spatially and temporally strongly limited to a few in situ measurements. Pond bathymetry, which is pond depth spatially fully resolved, remains unexplored. Here, we present a newly developed method to derive pond bathymetry from aerial images. We determine it from a photogrammetric multi-view reconstruction of the summer ice surface topography. Based on images recorded on dedicated grid flights and facilitated assumptions, we were able to obtain pond depth with a mean deviation of 3.5 cm compared to manual in situ observations. The method is independent of pond color and sky conditions, which is an advantage over recently developed radiometric airborne retrieval methods. It can furthermore be implemented in any typical photogrammetry workflow. We present the retrieval algorithm, including requirements for the data recording and survey planning, and a correction method for refraction at the air–pond interface. In addition, we show how the retrieved surface topography model synergizes with the initial image data to retrieve the water level of individual ponds from the visually determined pond margins. We use the method to give a profound overview of the pond coverage on the MOSAiC floe, on which we found unexpected steady pond coverage and volume. We were able to derive individual pond properties of more than 1600 ponds on the floe, including their size, bathymetry, volume, surface elevation above sea level, and temporal evolution. We present a scaling factor for single in situ depth measurements, discuss the representativeness of in situ pond measurements and the importance of such high-resolution data for new satellite retrievals, and show indications for non-rigid pond bottoms. The study points out the great potential to derive geometric properties of the summer sea ice surface emerging from the increasingly available visual image data recorded from uncrewed aerial vehicles (UAVs) or aircraft, allowing for an integrated understanding and improved formulation of the thermodynamic and hydrological pond system in models
