Alfred Wegener Institute for Polar and Marine Research
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Climate-driven changes in underwater irradiance and primary productivity in an Antarctic fjord (Potter Cove, Western Antarctic Peninsula)
Get PDFThe West Antarctic Peninsula (WAP) is a hotspot of climate warming, evidencing glacier retreat and a decrease in
the fast-ice duration. This study provides a > 30-y time-series (1987–2022) on annual and seasonal air temperatures in Potter Cove (Isla 25 de Mayo/King George Island). It investigates the interaction between warming,
glacial melt, fast-ice and the underwater conditions (light, salinity, temperature, turbidity) over a period of 10
years along the fjord axis (2010–2019), and for the first time provides a unique continuous underwater irradiance
time series over 5 years (2014–2018). The effects on the annual light budget in the water column were
studied along the fjord axis in three areas, a low glacier influence area (LGI), an intermediate glacier influence
area (IGI), and a high glacier influence area (HGI). To determine the possible impact of light limitation on the
viability of benthic primary producers, the minimum annual light requirements and the daily metabolic carbon
balance of two key macroalgal Antarctic species, Himantothallus grandifolius and Palmaria decipiens, wereestimated. The mean annual, autumn, winter and spring air temperature has risen during the last three decades, but summer temperatures kept rather stable. Turbidity caused by glacial melt mostly governs the underwater light climate while fast-ice duration is currently of minor importance for the annual light budget. Glacier melting differentially affected the fjord system along its axis. The three areas showed quantitative differences in turbidity and underwater irradiance varying across seasons and years. Water clarity significantly decreased within the last few years, with key macroalgal species probably not reaching their minimum annual light requirements during warmer years. This may have considerable effects on the primary productivity of the ecosystem
Unveiling pelagic-benthic coupling associated with the biological carbon pump in the Fram Strait (Arctic Ocean)
Get PDFAbstract
Settling aggregates transport organic matter from the ocean surface to the deep sea and seafloor. Though plankton communities impact carbon export, how specific organisms and their interactions affect export efficiency is unknown. Looking at 15 years of eDNA sequences (18S-V4) from settling and sedimented organic matter in the Fram Strait, here we observe that most phylogenetic groups were transferred from pelagic to benthic ecosystems. Chaetoceros socialis, sea-ice diatoms, Radiolaria, and Chaetognatha are critical components of vertical carbon flux to 200 m depth. In contrast, the diatom C. socialis alone is essential for the amount of organic carbon reaching the seafloor. Spatiotemporal changes in community composition show decreasing diatom abundance during warm anomalies, which would reduce the efficiency of a diatom-driven biological carbon pump. Interestingly, several parasites are also tightly associated with carbon flux and show a strong vertical connectivity, suggesting a potential role in sedimentation processes involving their hosts, especially through interactions with resting spores, which could have implications for pelagic-benthic coupling and overall ecosystem functioning.</jats:p
Reactivation of a Subglacial Channel Around the Grounding Zone of Roi Baudouin Ice Shelf, Antarctica
Get PDFSubglacial water beneath the Antarctic Ice Sheet is often funneled via subglacial channels, which inject freshwater into ice-shelf cavities where it interacts with ocean water. The temporal variability of this system has been poorly observed, but its importance for ice dynamics is well recognized. Airborne radar data show a subglacial channel evolving within a decade near of the grounding zone of the Roi Baudouin Ice Shelf (East Antarctica), while topographic signatures on the ice shelf indicate prior inactivity for 60 years. Combining our observations with subglacial hydrological modeling, we suggest that the interplay between episodic subglacial water pulses and ocean water intrusion drive the opening and closing of the channels. Our findings illuminate the short-term transient nature of subglacial channel activity. This impacts ice-shelf–ocean processes, which are important for constraining increasing ocean warming onto ice-shelf basal mass balance, but pose significant challenges for subglacial hydrological modeling at the grounding zone
A new perspective for revealing ‘hidden’ interactions in ecological networks
Get PDFEcological network models are essential for developing and quantifying ecosystem-based management strategies. Unobserved species interactions alter the interpretation of structural and functional characteristics of the ecosystem being studied. Link prediction algorithms can help to identify such unobserved, ‘hidden’ interactions. However, due to general unfamiliarity and insufficient ecological interpretations, the use of link prediction algorithms in ecology remains limited.
In this study, we enhance the link prediction applicability in ecological networks by considering and quantifying the algorithm results from the link as well as the node perspective using a coastal food web model from the northern Wadden Sea as a case study. For this purpose, we have defined the Weighted Unobserved Node Connectivity (WUNC) representing a new node property.
The WUNC facilitates the estimation of the missing connectivity of a species in relation to a considered original source network. Such a new combination of both link and node perspectives helps to uncover unobserved interactions as well as the resulting lack of species connectivity in poorly understood environments without active sampling.
The bi-dimensional perspective presented in this study provides a more effective use of link prediction algorithms to identify and prioritize under-connected species and their unobserved interactions. This enables the design of more targeted, species-specific measurement campaigns to validate predicted interactions, thereby supporting refinements of existing ecological network models. A more comprehensive representation of interactions in ecological network models contributes to more accurate modelling results and improves their interpretation to support better management strategies in times of environmental changes
The first recorded fish-killing bloom in the Beibu Gulf, China: caused by dinoflagellate Karenia selliformis
Get PDFThe Beibu Gulf is located in the northwestern South China Sea. On August 2, 2023, a mass mortality event of cultured Trachinotus ovatus occurred in Lianzhou Bay and Tieshan Bay, suspected to be associated with a Karenia bloom. To identify the causative organism, investigate possible environmental drivers for bloom development, and determine the cause of fish mortality, in-situ bloom samples were collected for community characterization and toxicity analysis. Results showed that during the bloom, seawater quality remained within China’s highest classification, Class I, and RDA analyses indicated that protistan communities were primarily influenced by dissolved inorganic nitrogen (DIN) and pH. Based on a combination of microscopic observation, phylogenetic analyses of ITS and D1-D3 rDNA sequences obtained from clone libraries, and 18S rDNA V4 amplicon sequence variant (ASV) analysis, all approaches confirmed Karenia selliformis as the bloom-causing organism. Weak westward sea surface winds before and during the period facilitated the accumulation and probably the bloom formation of K. selliformis in Lianzhou and Tieshan coastal waters. A rabbit erythrocyte lysis assay detected hemolytic toxicity of 45.2–48.3% in tests with 5 × 107 rabbit erythrocyte cells exposed to 1.3–2.5 × 104 K. selliformis cells, suggesting it as a predominant factor in fish mortality. LC-MS/MS analysis did not detect neurotoxic shellfish toxins (BTX2, BTX3), diarrhetic shellfish toxins (DTX1-2, OA), or SPX1. However, gymnodimine-A (GYM-A), a “fast-acting” toxin known to be exclusively produced by K. selliformis, was detected at 2.2–2.5 pg GYM-A cell-1. To our knowledge, this study represents the first recorded fish-killing caused by a K. selliformis bloom in Chinese waters. The study provides the first biological and toxicity insights into K. selliformis bloom, crucial for the management and mitigation of fish-killing events associated to harmful algal blooms (HABs) in the Beibu Gulf and the South China Sea
How we value the Coast - Arctic Coastal Ecosystem Services on Qikiqtaruk, Canada
Get PDFArctic coasts are strongly impacted by global climate change. While coastal erosion is one of the most visible consequences, changes in the supply and demand of ecosystem services (ES) are also having an increasingly significant effect on the communities living along these coasts. While the concept of ecosystem services is relevant, it is underutilized, particularly in Arctic regions.
In the scope of my PhD project, we will access in the first part the supply of ES on Qikiqtaruk (Herschel Island), Canada followed by stakeholder interviews to quantify the demand of coastal ES. This project will involve measuring physical and biological parameters, including permafrost and active layer temperatures, water quality (turbidity and salinity), and fish catches, with a particular focus on the condition of the fish. These measurements will help characterize the ecosystems present on the island. Combining these results with the stakeholder interviews and participatory mapping will provide a detailed overview of the use of, and need for, ecosystem services on the Arctic coast of Qikiqtaruk. The special role of the island as a Territorial Park, as well as its importance for traditional land use and education, will be considered, and we will try to co-produce outputs that can be used by the Herschel Island–Qikiqtaruk Rangers and inform potential policy decisions around the Territorial Park.
The future direction of this project will be shaped by consultation meetings with local stakeholders during the upcoming field season. One potential approach is to extend the assessment of coastal ecosystem service supply and demand to the wider Inuvialuit Settlement Region in order to address these issues on a regional scale
Larval Physiological Responses to Temperature Across the European Distribution Range of a Global Invader at Home: The Shore Crab Carcinus maenas
Get PDFABSTRACTIn marine species with complex life cycles, thermal tolerance is usually narrower in larvae than in adults. Hence, range contraction and expansion, as a consequence of climate change, may be enhanced or hampered by among‐population variability in the thermal tolerance of larval stages. We quantified the performance (i.e., survival, development, and growth) of larvae of the shore crab Carcinus maenas at different temperatures (range 9°C to 27°C in steps of 3°C) in populations located towards the limits of the European distribution range (South: Vigo, Spain; North: Bergen and Trondheim, Norway). We hypothesised that, given the geographical distance, larvae from northern populations would show increased tolerance to low temperatures while those from southern populations would show increased tolerance to high temperatures. Such patterns would enhance poleward range expansion and counteract contraction as compared with a scenario where thermal tolerance does not change along the latitudinal gradient. Populations from southern Europe (Spain) showed slightly increased survival at higher temperatures compared to those further north and in invasive North American populations. However, there was little variation in larval tolerance between populations of Northern Spain and Norway: survival and growth rates were low at temperatures 9°C and 27°C. Larvae from the northernmost European populations (Norway) showed significantly shorter duration of development at low temperatures, which might have an adaptive value, contingent on the actual pattern of temperatures experienced during the larval phase. Further range expansions (or contractions) are likely to be driven solely by increasing temperatures unless populations located right at the range limit show increased tolerance to low (or high) temperatures.</jats:p
Hydroclimatic development from the Early Holocene to anthropogenic times: a comparative study of diatom oxygen isotope records and multiproxy data from Lake Khamra, eastern Siberia
Get PDFNorthern Eurasia underwent major hydroclimatic changes since the beginning of the Holocene interglacial. A rapid warming period reaching the Holocene Thermal Maximum (HTM), followed by a general cooling trend until recent times, was observed in Eurasian lacustrine diatom oxygen isotope (δ18Odiatom) records. In this study, we present a new Holocene δ18Odiatom record from Lake Khamra (59.99°N, 112.98°E, Siberia). Our record aligns with Holocene δ18Odiatom records across the Northern Hemisphere, showing a general millennial-scale cooling trend following an initial maximum at 11.2 cal. ka BP and a second maximum at 6.7 cal. ka BP. These maxima correspond to the summer insolation maximum and elevated Northern Hemisphere air temperatures, as well as increased bioproductivity. Variability on centennial scales is likely driven by precipitation changes, which coincide with higher sedimentation rates and overlay the general decreasing trend throughout the Holocene. In addition, we compared two multiproxy datasets with decadal resolution from Lake Khamra, including δ18Odiatom data and biogeochemical proxies such as total organic carbon (TOC), total nitrogen (TN), stable carbon (δ13C) and nitrogen (δ15N) isotopes, and total mercury (THg). The datasets cover a ~210-year period (c. 6.140–6.350 cal. ka BP) at the end of the HTM and a recently published ~220-year record (c. 1790–2015 CE) that embraces the anthropogenic times. The comparison of these two warm phases reveals distinct differences in both the absolute values and the variability of the records. Regarding the δ18Odiatom data, the recent period shows a nearly threefold increase in range and double the standard deviation, suggesting greater hydroclimatic variability compared to the end of the HTM. Notably, THg levels indicate a sharp increase in recent decades, while δ13C declined, contrasting with the observations at the end of the HTM. We attribute these observations partially to far-reaching anthropogenic effects on remote lake systems
Thermokarst Lagoons: Distribution, Classification and Dynamics in Permafrost‐to‐Marine Transitions
Get PDFThe transition of permafrost landscapes to marine environments, driven by climate change, plays a crucial role in the global carbon cycle. Thermokarst lagoons, formed along permafrost coasts when thermokarst lakes get connected to the sea, are key features in this transition. Using remote sensing imagery, we manually mapped and classified 520 thermokarst lagoons along the coastline of five Arctic shelf seas (Laptev, East Siberian, Chukchi, Alaskan Beaufort and Canadian Beaufort seas) between the Taymyr and Tuktoyaktuk peninsulas, and most were located along the Canadian Beaufort Sea. These lagoons cover a total area of 3457 km², with strong regional variations in both size and distribution. Based on their sea connectivity, we categorised the lagoons into five classes, with 55% in early transition stages (very low to low connected). From 2000 to 2021, lagoon area increased in all regions, with the Alaska Beaufort Sea coast showing the most growth (+1.34%). Smaller and isolated lagoons expanded faster than those in lagoon systems or deltas. Our analysis links thermokarst lagoon distribution to coastal erosion, land cover, ground ice and organic carbon, showing that most lagoons are located in areas of thermokarst lake coverage and high coastal erosion. This unique pan‐Arctic dataset serves as a foundation for understanding thermokarst lagoon dynamics and their role in the rapidly changing Arctic environment
Impacts of air fraction increase on Arctic sea ice density, freeboard, and thickness estimation during the melt season
Get PDFArctic sea ice has undergone significant changes over the past 50 years. Modern large-scale estimates of sea ice thickness and volume come from satellite observations. However, these estimates have limited accuracy, especially during the melt season, making it difficult to compare the Arctic sea ice state year to year. Uncertainties in sea ice density lead to high uncertainties in ice thickness retrieval from its freeboard. During the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition, we observed a first-year ice (FYI) freeboard increase of 0.02 m, while its thickness decreased by 0.5 m during the Arctic melt season in June–July 2020. Over the same period, the FYI density decreased from 910 to 880 kg m−3, and the sea ice air fraction increased from 1 % to 6 %, due to air void expansion controlled by internal melt. This increase in air volume substantially affected FYI density and freeboard. Due to differences in sea ice thermodynamic state (such as salinity and temperature), the air volume expansion is less pronounced in second-year ice (SYI) and has a smaller impact on the density evolution of SYI and ridges. We validated our discrete measurements of FYI density from coring using co-located ice topography observations from underwater sonar and an airborne laser scanner. Despite decreasing ice thickness, a similar counterintuitive increasing ice freeboard was observed for the entire 0.9 km2 MOSAiC ice floe, with a stronger freeboard increase for FYI than for less saline SYI. The surrounding 50 km2 area experienced a slightly lower 0.01 m ice freeboard increase in July 2020, despite comparable 0.5 m melt rates obtained from ice mass balance buoys. The increasing sea ice air volume defines the rapid decrease in FYI density, complicates the retrieval of ice thickness from satellite altimeters during the melt season, and underlines the importance of considering air volume and density changes in retrieval algorithms