Alfred Wegener Institute for Polar and Marine Research
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Decadal Changes in the Pathways of the Atlantic Water Core in the Arctic Ocean Inferred From Transient Tracers
No full textThe Atlantic Water plays a major and increasing role in the heat budget of the Arctic Ocean (Atlantification). The pathways of Atlantic Water within the Arctic Ocean, and in particular their sensitivities to large-scale atmospheric patterns such as the Arctic Oscillation, remain unclear. In this study, we used the trace gases CFC-12 and (Formula presented.) to investigate the Atlantic Water pathways during different phases of the Arctic Oscillation. We calculated tracer ages for the temperature maximum of the Atlantic Water, focusing on repeated transects (1994, 2005, 2015) in the Amerasian Basin of the Arctic Ocean. During a positive phase of the Arctic Oscillation in 1994, tracer ages were low along the Chukchi shelf due to a strong coherent boundary current. In contrast, the ages were up to 10 years higher in 2015 without this coherent current during a mixed phase of the Arctic Oscillation. Further, we identified a discontinuity in the inflow between the Makarov Basin and the Canada Basin during this phase. Tracer ages were 10 years higher in the Canada Basin, suggesting a closed circulation without direct inflow in this region. Our tracer ages generally align with previously proposed circulation schemes and water ages, with major exceptions in 2015. We have shown that the tracer ages are applicable to identify decadal changes in the Atlantic Water core pathways in the central Arctic Ocean
NAQPMS-PDAF v2.0: a novel hybrid nonlinear data assimilation system for improved simulation of PM2.5 chemical components
Get PDFIdentifying PM2.5 chemical components is crucial for formulating emission strategies, estimating radiative forcing, and assessing human health effects. However, accurately describing spatiotemporal variations in PM2.5 chemical components remains a challenge. In our earlier work, we developed an aerosol extinction coefficient data assimilation (DA) system (Nested Air Quality Prediction Model System with the Parallel Data Assimilation Framework (NAQPMS-PDAF) v1.0) that was suboptimal for chemical components. This paper introduces a novel hybrid nonlinear chemical DA system (NAQPMS-PDAF v2.0) to accurately interpret key chemical components (SO42-, NO3-, NH4+, OC, and EC). NAQPMS-PDAF v2.0 improves upon v1.0 by effectively handling and balancing stability and nonlinearity in chemical DA, which is achieved by incorporating the non-Gaussian distribution ensemble perturbation and hybrid localized Kalman-nonlinear ensemble transform filter with an adaptive forgetting factor for the first time. The dependence tests demonstrate that NAQPMS-PDAF v2.0 provides excellent DA results with a minimal ensemble size of 10, surpassing previous reports and v1.0. A 1-month DA experiment shows that the analysis field generated by NAQPMS-PDAF v2.0 is in good agreement with observations, especially in reducing the underestimation of NH4+ and NO3- and the overestimation of SO42-, OC, and EC. In particular, the Pearson correlation coefficient (CORR) values for NO3-, OC, and EC are above 0.96, and the R2 values are above 0.93. NAQPMS-PDAF v2.0 also demonstrates superior spatiotemporal interpretation, with most DA sites showing improvements of over 50 %-200 % in CORR and over 50 %-90 % in RMSE for the five chemical components. Compared to the poor performance in the global reanalysis dataset (CORR: 0.42-0.55, RMSE: 4.51-12.27 μg m-3) and NAQPMS-PDAF v1.0 (CORR: 0.35-0.98, RMSE: 2.46-15.50 μg m-3), NAQPMS-PDAF v2.0 has the highest CORR of 0.86-0.99 and the lowest RMSE of 0.14-3.18 μg m-3. The uncertainties in ensemble DA are also examined, further highlighting the potential of NAQPMS-PDAF v2.0 for advancing aerosol chemical component studies
Pan‐Arctic Assessment of Coastal Settlements and Infrastructure Vulnerable to Coastal Erosion, Sea‐Level Rise, and Permafrost Thaw
No full textAbstractThis study assesses the vulnerability of Arctic coastal settlements and infrastructure to coastal erosion, Sea‐Level Rise (SLR) and permafrost warming. For the first time, we characterize coastline retreat consistently along permafrost coastal settlements at the regional scale for the Northern Hemisphere. We provide a new method to automatically derive long‐term coastline change rates for permafrost coasts. In addition, we identify the total number of coastal settlements and associated infrastructure that could be threatened by marine and terrestrial changes using remote sensing techniques. We extended the Arctic Coastal Infrastructure data set (SACHI) to include road types, airstrips, and artificial water reservoirs. The analysis of coastline, Ground Temperature (GT) and Active Layer Thickness (ALT) changes from 2000 to 2020, in addition with SLR projection, allowed to identify exposed settlements and infrastructure for 2030, 2050, and 2100. We validated the SACHI‐v2, GT and ALT data sets through comparisons with in‐situ data. 60% of the detected infrastructure is built on low‐lying coast (10 m a.s.l). The results show that in 2100, 45% of all coastal settlements will be affected by SLR and 21% by coastal erosion. On average, coastal permafrost GT is increasing by 0.8°C per decade, and ALT is increasing by 6 cm per decade. In 2100, GT will become positive at 77% of the built infrastructure area. Our results highlight the circumpolar and international amplitude of the problem and emphasize the need for immediate adaptation measures to current and future environmental changes to counteract a deterioration of living conditions and ensure infrastructure sustainability.</jats:p
Integrating the needs of recovering populations of baleen whales into the revised management framework for the commercial fishery for Antarctic krill
Get PDFWe consider how the ongoing recovery of baleen whale populations requires revised considerations when managing the largest commercial fishery in the Southern Ocean: the fishery for Antarctic krill (Euphausia superba). Baleen whales already represent one of the major consumers of krill, and as such compete with the fishery, yet they are not explicitly included in the monitoring programme or krill fisheries management plan of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Individual baleen whales are at direct mortality risk from ship strikes, entanglement and by-catch. In addition, sub-lethal impacts on individuals, but with population-level consequences via decreased body condition and reproductive rates, may arise from local depletion of prey and prey field disturbance that increases whale energetic costs. Mitigating these risks requires that baleen whales, including those species not yet recovered, are fully integrated into management procedures. A vital issue will be to facilitate the ongoing recovery of blue, fin and sei whales, populations of which are still heavily depleted relative to their pre-whaling abundance. Part of the answer to this will be how CCAMLR resolves outstanding issues related to its newly emerging revised krill fishery management framework. Management of the krill fishery is data-poor, with much of the scientific support reliant upon data that are now decades old. The decision rules used to determine sustainable yields also require close scrutiny, given that they were negotiated at a time when baleen whales were rarely observed and krill fishery catches were low in relation to the estimated available krill biomass. The Antarctic marine ecosystem is spatially and temporally dynamic, and is changing, yet CCAMLR still assumes a static system. An explicit commitment to collect up-to-date monitoring data about krill and baleen whales is vital to help inform the revised management framework. Precaution argues that catch levels should not increase until adequate data are available for effective management. Knowledge about the status of baleen whales will inevitably require close collaboration with the International Whaling Commission (IWC)
Hepatic Transcriptomic Responsiveness of Polar Cod, Boreogadus saida, to Ocean Acidification and Warming
Get PDFBackground: This study was part of a larger comprehensive project (BIOACID) addressing the physiological resilience of Polar cod, Boreogadus saida, to ocean acidification and global warming and aimed to unravel underlying molecular mechanisms of the observed physiological responses. Methods: Fish were acclimated long-term to three CO2 concentrations comprising control conditions (390 ppm) and two projected climate scenarios (780 ppm and 1170 ppm). Each CO2 treatment was combined with four temperatures: 0, 3, 6, and 8 °C. Here, we focused on the hepatic transcriptomic profiles from these previously physiologically characterized fish. Results: Generally, we did not detect signs of a classical stress response. Consistent with functional observations, warming induced much stronger molecular responses compared to elevated PCO2, but an interaction between both factors existed to some extent. Gene ontology analysis revealed a strong response in lipid, amino acid, and protein metabolism. With increasing temperature, we observed a shift away from lipid metabolism, while carbohydrate metabolic pathways remained stable. Conclusions: Although we found Polar cod to be quite resilient to ocean acidification, temperature will remain a critical parameter for this valuable Arctic keystone species, and the question remains as to whether the observed acclimation strategies can be implemented in its natural habitat, especially when food supply is limited
Circum-Antarctic bottom water formation mediated by tides and topographic waves
No full textThe downslope plumes of dense shelf water (DSW) are critical for the formation of Antarctic Bottom Water (AABW), and thus to the exchange of heat and carbon between surface and abyssal ocean. Previous studies have shown that tides and overflow-forced topographic Rossby waves (TRWs) may have strong impact on the downslope transport of DSW, but it remains unclear how the combined action of these two processes influence the descent processes of DSW, and of the resulting AABW properties. Here, with a synthesis of historical in situ observations and a set of numerical model experiments, we show that tides and TRWs play comparable roles in AABW formation: they both act to accelerate DSW descent to the abyss, leading to the formation of colder and denser AABW. Yet, tides have little impact on AABW formation unless the continental slope is steep enough to suppress TRW generation. We further characterize the dynamical regimes of dense overflows around the entire Antarctic continent based on the relative importance of TRWs versus tides. These findings highlight the pervasive role of high-frequency processes, which are not well represented in the present climate models, in the formation of AABW, and thus in the global overturning circulation
Different temperature sensitivities of key physiological processes lead to divergent trait response patterns in Arctic phytoplankton
Get PDFOcean warming is especially pronounced in the Arctic, and phytoplankton will face thermodynamically
driven changes in their physiology, potentially pushing them beyond their thermal optimum. We assessed temperature
responses of multiple functional traits over their entire thermal window (growth rates, quotas of particulate
organic carbon, nitrogen, and chlorophyll a, as well as photophysiological parameters) in three different
Arctic phytoplankton species (Thalassiosira hyalina, Micromonas pusilla, and Nitzschia frigida). Temperature
response patterns in growth and biomass production rates indicated that all species exhibit wide thermal windows
with highest rates at temperatures that exceed current polar temperatures. Species showed different temperature
response patterns in cellular elemental quotas, which originate from the interplay of cell division and
biomass production: These processes differ in their temperature sensitivity and optima, resulting in U-shaped,
bell-shaped, or linear patterns of elemental quotas. Despite unaltered light intensity, higher temperatures
increased light acclimation indices in all species while lifetimes of photosystem II reopening decreased in all
species, suggesting that warming causes a transition from light saturation to light limitation. Our findings on
temperature sensitivities of cell division and biomass production not only indicate that Arctic phytoplankton
may benefit from moderate warming, but also highlight that meaningful interpretations of cellular quotas
require a consideration of the underlying processes
Microbial growth in a warming Arctic: Exploring controls and temperature responses in permafrost soils
Get PDFPermafrost soils are particularly vulnerable to climate warming. With ~1,500&#160;Gt Carbon&#160;(C), they store a significant proportion of global soil C. Organic matter that was frozen and thus unavailable for microbial decomposition for millennia, is now thawing. How much of this permafrost C is decomposed will be determined by microbial activities and the partitioning of assimilated C to microbial growth (potential C stabilization) or microbial respiration (C loss). Our current knowledge on the controls of microbial growth and respiration in permafrost soils is, however, limited.
The objective of this study was to analyze microbial growth and respiration in permafrost soils and to explore soil organic matter composition, microbial community composition and various soil parameters as potential drivers. We collected 81 soil samples from four soil layers (organic, mineral, cryoturbated, permafrost) and three lowland tundra polygon types (low-center, flat-center, high-center) in Arctic Canada. We used pyrolysis-GC-MS fingerprinting to characterize soil organic matter composition and amplicon sequencing (16S, ITS1) to identify archaeal, bacterial, and fungal community composition. Temperature responses (Q10) were analyzed in an 8-week laboratory incubation experiment, subjecting soil aliquots to 4 &#176;C and 14 &#176;C. Microbial growth was determined by 18O-H2O-incorporation into DNA and microbial respiration by gas analysis.
Soil organic matter composition differed between soil layers along a gradient of degradation and C content. Organic matter complexity and diversity decreased with the level of decomposition. We found distinct soil organic matter composition for each polygon type, including all soil layers, suggesting different decomposition pathways, induced by differences in vegetation and soil water regime. Anoxic conditions in low-center polygons resulted in more archaea and distinct fungal communities. Microbial community composition differed among all soil layers, with particularly more fungi in organic soils. Microbial mass-specific growth and respiration differed among polygons and soil layers, and both increased with warming. Overall, temperature responses (Q10) were higher for respiration than for growth, implying that microbes are less efficient in using C for growth. Linear mixed effect models revealed that soil organic matter composition and microbial community composition were good predictors for mass-specific growth at field and warmed conditions. Mass-specific respiration was best explained by microbial community composition. Our predictors, however, did not explain the temperature responses.
Our results indicate that under warming, microbes allocated more C to respiration, leading to increased greenhouse gas emissions per unit of carbon taken up. We found these results while including all soil layers and polygon types, suggesting these responses to be representative for lowland Arctic ecosystems. Moreover, we could show that organic matter composition and microbial community composition are good predictors for microbial growth and respiration, thus deserving more attention in future studies.
This study is part of the EU H2020 project &#8220;Nunataryuk&#8221;.</jats:p
Climatic pacing of extreme Nile floods during the North African Humid Period
No full textUnderstanding how large river systems will respond to an invigorated hydrological cycle as simulated under higher global temperatures is a pressing issue. Insights can be gained from studying past wetter-than-present intervals, such as the North African Humid Period during the early Holocene Epoch (~11–6 thousand years ago). Here we present a 1,500-year-long annually laminated (varved) offshore sediment record that tracks the seasonal discharge of the Nile River during the North African Humid Period. The record reveals mobilization of large amounts of sediments during strong summer floods that may have rendered the Nile valley uninhabitable. More frequent and rapid transitions between extremely strong and weak floods between 9.2 and 8.6 thousand years ago indicate highly instable fluvial dynamics. Climate simulations suggest flood variability was paced by El Niño/Southern Oscillation on interannual timescales, while multi-decadal oscillatory modes drove changes in extreme flood events. These pacemakers have also been identified in the Nile flow records from the Common Era, which implies their stationarity under contrasting hydroclimatic conditions
