Alfred Wegener Institute for Polar and Marine Research
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Destructive fishing: An expert‐driven definition and exploration of this quasi‐concept
Get PDFAbstractNumerous policy and international frameworks consider that “destructive fishing” hampers efforts to reach sustainability goals. Though ubiquitous, “destructive fishing” is undefined and therefore currently immeasurable. Here we propose a definition developed through expert consultation: “Destructive fishing is any fishing practice that causes irrecoverable habitat degradation, or which causes significant adverse environmental impacts, results in long‐term declines in target or nontarget species beyond biologically safe limits and has negative livelihood impacts.” We show strong stakeholder support for a definition, consensus on many biological and ecological dimensions, and no clustering of respondents from different sectors. Our consensus definition is a significant step toward defining sustainable fisheries goals and will help interpret and implement global political commitments which utilize the term “destructive fishing.” Our definition and results will help reinforce the Food and Agricultural Organization's Code of Conduct and meaningfully support member countries to prohibit destructive fishing practices.</jats:p
Highly stratified mid-Pliocene Southern Ocean in PlioMIP2
Get PDFDuring the mid-Pliocene warm period (mPWP; 3.264–3.025 Ma), atmospheric CO2 concentrations were approximately 400 ppm, and the Antarctic Ice Sheet was substantially reduced compared to today. Antarctica is surrounded by the Southern Ocean, which plays a crucial role in the global oceanic circulation and climate regulation. Using results from the Pliocene Model Intercomparison Project (PlioMIP2), we investigate Southern Ocean conditions during the mPWP with respect to the pre-industrial period. We find that the mean sea surface temperature (SST) warming in the Southern Ocean is 2.8 °C, while global mean SST warming is 2.4 °C. The enhanced warming is strongly tied to a dramatic decrease in sea ice cover over the mPWP Southern Ocean. We also see a freshening of the ocean (sub)surface, driven by an increase in precipitation over the Southern Ocean and Antarctica. The warmer and fresher surface leads to a highly stratified Southern Ocean that can be related to weakening of the deep abyssal overturning circulation. Sensitivity simulations show that the decrease in sea ice cover and enhanced warming is largely a consequence of the reduction in the Antarctic Ice Sheet. In addition, the mPWP geographic boundary conditions are responsible for approximately half of the increase in mPWP SST warming, sea ice loss, precipitation, and stratification increase over the Southern Ocean. From these results, we conclude that a strongly reduced Antarctic Ice Sheet during the mPWP has a substantial influence on the state of the Southern Ocean and exacerbates the changes that are induced by a higher CO2 concentration alone. This is relevant for the long-term future of the Southern Ocean, as we expect melting of the western Antarctic Ice Sheet in the future, an effect that is not currently taken into account in future projections by Coupled Model Intercomparison Project (CMIP) ensembles
Historical Agrarian Change and its Connections to Contemporary Agricultural Extension in Northwest Cambodia
Get PDFThis historical overview uses a political ecology approach to examine agricultural change over time in Northwest Cambodia. It focuses on key historical periods, actors, and processes that continue to shape power, land, and farming relations in the region, emphasizing the relevance of this history for contemporary investments in agricultural extension services and research as part of the Zero Hunger by 2030 policy agenda for achieving the Sustainable Development Goals (SDG). Agricultural extension projects need to engage critically with historically complex and dynamic power, land, and farming relations–not only as the basis of social relations but as central to understanding the contemporary manifestation of farmer decision making and practice. Initiatives such as the SDGs replicate long histories of externally driven power-relations that orient benefits from changed practices towards elites in urban centers or distant global actors. Efforts to realize zero hunger by 2030 are endangered by neglect for the path-dependency of power-land-farming relations, which stretch from the past into the present to structure farmer decision making and practices
Carbon isotopes in the marine biogeochemistry model FESOM2.1-REcoM3
Get PDFAbstract. In this paper we describe the implementation of the carbon isotopes 13C and 14C (radiocarbon) into the marine biogeochemistry model REcoM3. The implementation is tested in long-term equilibrium simulations where REcoM3 is coupled with the ocean general circulation model FESOM2.1, applying a low-resolution configuration and idealized climate forcing. Focusing on the carbon-isotopic composition of dissolved inorganic carbon (δ13CDIC and Δ14CDIC), our model results are largely consistent with reconstructions for the pre-anthropogenic period. Our simulations also exhibit discrepancies, e.g. in upwelling regions and the interior of the North Pacific. Some of these differences are due to the limitations of our ocean circulation model setup, which results in a rather shallow meridional overturning circulation. We additionally study the accuracy of two simplified modelling approaches for dissolved inorganic 14C, which are faster (15 % and about a factor of five, respectively) than the complete consideration of the marine radiocarbon cycle. The accuracy of both simplified approaches is better than 5 %, which should be sufficient for most studies of Δ14CDIC.
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Rich microbial and depolymerising diversity in Antarctic krill gut.
Get PDFABSTRACT
With almost a quadrillion individuals, the Antarctic krill processes five million tons of organic carbon every day during austral summer. This high carbon flux requires a broad range of hydrolytic enzymes to decompose the diverse food-derived biopolymers. While krill itself possesses numerous such enzymes, it is unclear, to what extent the endogenous microbiota contribute to the hydrolytic potential of the gut environment. Here we applied amplicon sequencing, shotgun metagenomics, cultivation, and physiological assays to characterize the krill gut microbiota. The broad bacterial diversity (273 families, 919 genera, and 2,309 species) also included a complex potentially anaerobic sub-community. Plate-based assays with 198 isolated pure cultures revealed widespread capacities to utilize lipids (e.g., tributyrin), followed by proteins (casein) and to a lesser extent by polysaccharides (e.g., alginate and chitin). While most isolates affiliated with the genera
Pseudoalteromonas
and
Psychrobacter
, also
Rubritalea
spp. (Verrucomicrobia) were observed. The krill gut microbiota growing on marine broth agar plates possess 13,012 predicted hydrolyses; 15-fold more than previously predicted from a transcriptome-proteome compendium of krill. Cultivation-independent and -dependent approaches indicated members of the families
Flavobacteriaceae
and
Pseudoalteromonadaceae
to dominate the capacities for lipid/protein hydrolysis and to provide a plethora of carbohydrate-active enzymes, sulfatases, and laminarin- or porphyrin-depolymerizing hydrolases. Notably, also the potential to hydrolyze plastics such as polyethylene terephthalate and polylactatide was observed, affiliating mostly with Moraxellaceae. Overall, this study shows extensive microbial diversity in the krill gut, and suggests that the microbiota likely play a significant role in the nutrient acquisition of the krill by enriching its hydrolytic enzyme repertoire.
IMPORTANCE
The Antarctic krill (
Euphausia superba
) is a keystone species of the Antarctic marine food web, connecting the productivity of phyto- and zooplankton with the nutrition of the higher trophic levels. Accordingly, krill significantly contributes to biomass turnover, requiring the decomposition of seasonally varying plankton-derived biopolymers. This study highlights the likely role of the krill gut microbiota in this ecosystem function by revealing the great number of diverse hydrolases that microbes contribute to the krill gut environment. The here resolved repertoire of hydrolytic enzymes could contribute to the overall nutritional resilience of krill and to the general organic matter cycling under changing environmental conditions in the Antarctic sea water. Furthermore, the krill gut microbiome could serve as a valuable resource of cold-adapted hydrolytic enzymes for diverse biotechnological applications.
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Is spring melting in the Arctic detectable by under-ice radiation?
Get PDFA trend towards earlier sea-ice melt is detected in many ice-covered regions in the Arctic. The timing of the melt onset has a strong impact on the sea-ice energy budget. Melt onset changes the radiative properties of the ice due to increasing snow wetness and meltwater. So far, satellite passive microwave data are used to detect the melt onset. We analyzed transmitted radiation spectra as collected underneath drifting sea-ice using a remotely operated vehicle during the ARTofMELT expedition in the Fram Strait in spring 2023. We colocated those spectra with measurements of snow depth, sea ice and surface topography, chlorophyll-a concentration in the water column, and with aerial images. This combined dataset enables us to track down possible subsurface pathways and accumulation pools of meltwater. Areas of low snow load and depressed surface topography are characterized by higher transmitted radiation compared to areas with a thick snow cover. Those areas overlapped with areas that showed the first signs of surface melt. Chlorophyll-a concentrations varied only slightly in magnitude and did not match with the heterogeneous pattern of snow depth and ice topography. Here we discuss how to disentangle the influences of chlorophyll a and the subsurface meltwater on the spectral shape of transmitted radiation. We propose that upon successful disentanglement, the spectra can be used as an indicator for subsurface melting. Our study suggests that sea-ice melting starts subsurface and that measurements of transmitted solar radiation spectra could be used to identify the melt onset prior to surface melting. This can provide an interesting complementary information on melt occurrence and on the location of the water in the snowpack in addition to satellite passive microwave data
Cladoceran assemblages of the Last Interglacial obtained from permafrost lacustrine deposits exposed at the Laptev Sea coast
Get PDFThe cladoceran assemblages of the lacustrine deposits of the Krest-Yuryakh sequence (Marine Isotope Stage 5e, MIS5e; Last Interglacial, LIG) exposed at the southern coast of Bol’shoy Lyakhovsky Island and the Oyogos Yar mainland coast along the Dmitry Laptev Strait (Yakutia, Siberia, Russia) were investigated. Field studies on both sides of the Laptev Strait were conducted in 2002, 2007, and 2014. The vegetation of the study area is currently represented by Arctic tundra. The mean air temperature of the warmest month of the year (MTWA) is 3.5 °C for the studied sites on Bol’shoy Lyakhovsky Island and 6.9 °C for Oyogos Yar (https://www.worldclim.org; Fick and Hijmans, 2017). Age information of the Krest-Yuryakh lacustrine deposits is based on infrared-stimulated luminescence (IRSL) (Schirrmeister et al., submitted). Cladocera were studied in profile L7-11 on Bol’shoy Lyakhovsky Island and in profiles Oya-3-11, Oy7-01, Oy7-08, Oya 5-1 on Oyogos Yar.?
The studied fossil cladocera remains of Krest-Yuryakh deposits are exceptionally well preserved. The overall cladocera record comprises 13 taxa. The most common species are Chydorus cf. sphaericus, Bosmina sp. and Daphnia pulex gr. The cladoceran assemblages are dominated by littoral shallow-water taxa, such as Chydorus cf. sphaericus, Alona guttata / Coronatella rectangula. However, profile L7-11 on Bol’shoy Lyakhovsky had very low concentrations of specimens of which Chydorus cf. sphaericus is the most common species.
The cladoceran records on Oyogos Yar are more diverse and had much higher concentrations than those on Bol’shoy Lyakhovsky. Most of the cladoceran remains on Oyogos Yar belong to littoral phytophilous species, associated with macrophytes. In the cladoceran communities of Oyogos Yar, along with cold-water taxa, also more thermophilic taxa were found. In particular, the findings of remains of the species L. leidigi indicate much warmer conditions in the past than today. According to Flößner (2000), this species is absent nowadays in the arctic-subarctic zones, but present in the boreal zone. Thus, the modern distribution of L. leidigi is located considerably further south today. The northernmost known discovery of this species in Yakutia (northern Russia) is located in the basin of the Omoloy River (MTWA of +11.5 °C, Frolova & Nigmatullin, unpublished data).We conclude that the climatic conditions were more favorable for cladocerans on Oyogos Yar than on Bol’shoy Lyakhovsky in the Last Interglacial (LIG) sub-stage. The cladoceran assemblages of Oyogos Yar indicate lacustrine habitats with a well-developed vegetated littoral zone as well pelagic open-water zones in the paleo-lakes. Discoveries of cladoceran taxa significantly north of their modern ranges allow the reconstruction of warmer climatic conditions during LIG. Presumably, on Oyogos Yar, the mean temperature of the warmest month (MTWA) was at least ~4.5°C higher than today, which is supported by independent proxy-based - temperature reconstructions such as plant macro-fossils, pollen, and chironomids (Kienast et al., 2011) as well as by climate modeling simulations (Schirrmeister et al., submitted)
