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Shark conservation requires mortality-limiting regulations amid global change
No full textDespite anti-finning laws aimed at conserving sharks, Worm et al. have revealed that global shark mortality rates have surprisingly risen over the past decade, driven in large part by increased demand for meat. Here, we discuss the importance of this study, underscoring the need for broader regulations addressing overall shark mortality amid threats from global chang
Central Arctic Ocean surface–atmosphere exchange of CO2 and CH4 constrained by direct measurements
Get PDFThe central Arctic Ocean (CAO) plays an important role in the global carbon cycle, but the current and future exchange of the climate-forcing trace gases methane(CH4) and carbon dioxide (CO2) between the CAO and the atmosphere is highly uncertain. In particular, there are very few observations of near-surface gas concentrations or direct air–sea CO2 flux estimates and no previously reported direct air–sea CH4 flux estimates from the CAO. Furthermore, the effect of sea ice on the exchange is not well understood. We present direct measurements of the air–sea flux of CH4 and CO2, as well as air–snow fluxes of CO2 in the summertime CAO north of 82.5◦ N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021.
Measurements of air–sea CH4 and CO2 flux were made
using floating chambers deployed in leads accessed from
sea ice and from the side of Oden, and air–snow fluxes
were determined from chambers deployed on sea ice. Gas
transfer velocities determined from fluxes and surface-water-dissolved gas concentrations exhibited a weaker wind speed dependence than existing parameterisations, with a median sea-ice lead gas transfer rate of 2.5 cm h−1
applicable over the observed 10 m wind speed range (1–11 m s−1 ). The average observed air–sea CO2 flux was −7.6 mmolm−2 d −1, and the average air–snow CO2 flux was −1.1 mmolm−2 d −1. Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of −1.75 mmolm−2 d −1, within the range of previous indirect estimates.The average observed air–sea CH4 flux of 3.5 µmolm−2 d−1, accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35 µmolm−2 d−1, lower than previous estimates and implying that the CAO is a very small (- 1 %) contributor to the Arctic flux of CH4 to the atmosphere
Vertical mixing alleviates autumnal oxygen deficiency in the central North Sea
Get PDFThere is an immediate need to better understand and monitor shelf sea dissolved oxygen (O2) concentrations. Here we use high-resolution glider observations of turbulence and O2 concentrations to directly estimate the vertical O2 flux into the bottom mixed layer (BML) immediately before the autumn breakdown of stratification in a seasonally stratified shelf sea. We present a novel method to resolve the oxycline across sharp gradients due to slow optode response time and optode positioning in a flow “shadow zone” on Slocum gliders. The vertical O2 flux to the low-O2 BML was found to be between 2.5 to 6.4 mmol m−2 d−1. Episodic intense mixing events were responsible for the majority (up to 90 %) of this oxygen supply despite making up 40 % of the observations. Without these intense mixing events, BML O2 concentrations would approach ecologically concerning levels by the end of the stratified period. Understanding the driving forces behind episodic mixing and how these may change under future climate scenarios and renewable energy infrastructure is key for monitoring shelf sea health
Environmental control and metabolic strategies of organic-matter-responsive bacterioplankton in the Weddell Sea (Antarctica)
No full textHeterotrophic microbial communities play a significant role in driving carbon fluxes in marine ecosystems. Despite their importance, these communities remain understudied in remote polar oceans, which are known for their substantial contribution to the biological drawdown of atmospheric carbon dioxide. Our research focused on understanding the environmental factors and genetic makeup of key bacterial players involved in carbon remineralization in the Weddell Sea, including its coastal polynyas. Our experiments demonstrated that the combination of labile organic matter supply and temperature increase synergistically boosted bacterial growth. This suggests that, besides low seawater temperature, carbon limitation also hinders heterotrophic bacterial activity. Through the analysis of metagenome-assembled genomes, we discovered distinct genomic adaptation strategies in Bacteroidia and Gammaproteobacteria, both of which respond to organic matter. Both natural phytoplankton blooms and experimental addition of organic matter favoured Bacteroidia, which possess a large number of gene copies and a wide range of functional membrane transporters, glycoside hydrolases, and aminopeptidases. In contrast, the genomes of organic-matter-responsive Gammaproteobacteria were characterized by high densities of transcriptional regulators and transporters. Our findings suggest that bacterioplankton in the Weddell Sea, which respond to organic matter, employ metabolic strategies similar to those of their counterparts in temperate oceans. These strategies enable efficient growth at extremely low seawater temperatures, provided that organic carbon limitation is alleviate
The influence of pre-exposure to marine heatwaves on the critical thermal maxima (CTmax) of marine foundation species
No full text1. Marine foundation species underpin some of the world's most diverse ecosystems but they are increasingly threatened by intensification of marine heatwaves (MHWs). Where MHWs exceed critical thermal maxima (CTmax), increased mortality and population declines can occur. CTmax is increasingly used to assess MHW population vulnerability but studies estimating CTmax across species, range edges and thermal histories in a comparable manner remain lacking.
2. We determined the impact of MHWs on subsequent CTmax estimates of matched cool/warm affinity pairs of marine foundation species (kelp, seagrass and bivalves) in the Western English Channel. Following a 4-week MHW simulation, individuals were subjected to a CTmax trial, where temperatures were raised by 2°C day−1 until physiological end points were reached.
3. We found no positive effect of MHWs on CTmax but clear negative impacts were observed for some groups of foundation species. Increased MHW intensity had a stepwise negative impact on the physiology of both warm (Laminaria ochroleuca) and cool water (L. digitata) kelp species that manifested in significant reductions in CTmax. Surprisingly, this was most marked in the warm water species, which runs opposite to the assumed safety of leading-edge populations. The physiology of warm (Zostera noltii) and cool (Z. marina) seagrasses was negatively impacted by increasing MHW intensity but no significant decrease in CTmax was observed. Both bivalve species (Mytilus edulis and Magallana gigas) showed marked resistance to exposure to MHWs, which was unexpected given the observed vulnerability of these species to stressful summertime conditions.
4. Our results show pre-exposure to realistic MHWs can influence CTmax values but generalities are difficult to make across groups or based on assumed thermal safety margins. We show CTmax is a labile trait and exposure to MHWs, can erode the resilience of an individual or population to subsequent thermal challenges. This leaves uncertainty within frameworks built to understand where and when MHWs will be most impactful.
5. Further experimentation across a wider range of species and thermal challenges is needed to better understand the dynamic nature of CTmax and field validation is needed to determine the responses of individuals and populations within complex natural systems
Functional responses of a medium-ranging marine predator highlight the importance of frontal zones as foraging locations
Get PDFThe distribution of marine predators is linked to bio-physical processes that structure the spatio-temporal availability of prey species. Within shelf seas, tidal fronts are highly productive regions occurring at the interface between mixed and stratified waters. Fronts are predictable but dynamic features, with their timing and strength varying seasonally and annually. The availability of frontal habitats will also vary between animal populations depending on geographic location. Thus, understanding the associations between marine predators and frontal habitats across a range of environmental conditions will assist marine management and conservation. Here, we assessed functional responses of breeding black-legged kittiwakes Rissa tridactyla to environmental covariates related to tidal fronts (front strength, distance to fronts, sea surface temperature [SST] and surface chlorophyll concentration) from 10 UK colonies located throughout the North Sea. Kittiwakes showed a tendency to forage in areas of higher, but not maximal, front strength when such areas were available. Areas closer to fronts (<10 km) were selected when available, though we also observed increased usage of areas distant from fronts (30-50 km). Kittiwakes tended to forage in cooler, mixed waters, particularly as average SST rose. When average chlorophyll concentrations were low, habitat usage peaked in areas of higher chlorophyll. The results highlight the importance of frontal habitats and the dynamic, non-linear nature of seabird responses to habitat. Accounting for dynamic changes in habitat availability will play a key role in future conservation efforts, particularly as marine renewable installations and climate change may influence water stratification patterns
Habitat preferences of Phoebetria albatrosses in sympatry and allopatry
Get PDFCompetition is often proposed to drive niche segregation along multiple axes in speciose communities. Understanding spatial partitioning of foraging areas is particu�larly important in species that are constrained to a central place. We present a natural experiment examining variation in habitat preferences of congeneric Southern Ocean predators in sympatry and allopatry. Our aim was to ascertain consistency of habitat preferences within species, and to test whether preferences changed in the presence of the congener
Measurements of particulate methanesulfonic acid above the remote Arctic Ocean using a high resolution aerosol mass spectrometer
Get PDFMethanesulfonic acid (MSA) is an important product from the oxidation of dimethyl sulfide (DMS), and thus is
often used as a tracer for marine biogenic sources and secondary organic aerosol. MSA also contributes to aerosol
mass and potentially to the formation of cloud condensation nuclei and new particles. However, measurements of
MSA at high temporal resolution in the remote Arctic are scarce, which limits our understanding of its formation,
climate change impact and regional transport. Here, we applied a validated quantification method to determine
the mass concentration of MSA and non-sea salt sulfate (nss-SO4) in PM2.5 in the marine boundary layer, using a
high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) during a research cruise to the Arctic and
North Atlantic Ocean, between 55 ◦N and 68 ◦N (26th May to June 23, 2022). With this method, the concen�trations of MSA in the remote Arctic marine boundary layer were determined for the first time. Results show that
the average MSA concentration was 0.025 ± 0.03 μg m− 3
, ranging from <0.01 to 0.32 μg m− 3
. The lowest MSA
level was found towards the northern leg of the cruise (near Sisimut (67 ◦N)) with air masses from sea ice over
the northern polar region, and the highest MSA concentrations were observed over the Atlantic open ocean. The
diurnal cycles of gas MSA, particulate MSA and nss-SO4 peaked in the afternoon, about one hour later than that of
peak of solar radiation, which suggests that photochemical process is an important mechanism for the conversion
of DMS into MSA above the remote ocean. The mass ratio of MSA to nss-SO4 (MSA/nss-SO4) presents a tem�perature dependence, which indicates that the addition branching pathway favors MSA formation, while thermal decay of intermediate radicals could be a possible pathway for sulfate formation. Finally, we found that the MSA/ nss-SO4 ratio is around 0.22-0.25 in the remote northern marine atmosphere
Has Reducing Ship Emissions Brought Forward Global Warming?
Get PDFShips brighten low marine clouds from emissions of sulfur and aerosols, resulting in visible “ship tracks”. In 2020, new shipping regulations mandated an ∼80% reduction in the allowed fuel sulfur content. Recent observations indicate that visible ship tracks have decreased. Model simulations indicate that since 2020 shipping regulations have induced a net radiative forcing of +0.12 Wm−2. Analysis of recent temperature anomalies indicates Northern Hemisphere surface temperature anomalies in 2022–2023 are correlated with observed cloud radiative forcing and the cloud radiative forcing is spatially correlated with the simulated radiative forcing from the 2020 shipping emission changes. Shipping emissions changes could be accelerating global warming. To better constrain these estimates, better access to ship position data and understanding of ship aerosol emissions are needed. Understanding the risks and benefits of emissions reductions and the difficultly in robust attribution highlights the large uncertainty in attributing proposed deliberate climate intervention
Diatoms exhibit dynamic chloroplast calcium signals in response to high light and oxidative stress
No full textDiatoms are a group of silicified algae that play a major role in marine and freshwater ecosystems. Diatom chloroplasts were acquired by secondary endosymbiosis and exhibit important structural and functional differences from the primary plastids of land plants and green algae. Many functions of primary plastids, including photoacclimation and inorganic carbon acquisition, are regulated by calcium-dependent signaling processes. Calcium signaling has also been implicated in the photoprotective responses of diatoms; however, the nature of calcium elevations in diatom chloroplasts and their wider role in cell signaling remains unknown. Using genetically encoded calcium indicators, we find that the diatom Phaeodactylum tricornutum exhibits dynamic calcium elevations within the chloroplast stroma. Stromal calcium ([Ca2+]str) acts independently from the cytosol and is not elevated by stimuli that induce large cytosolic calcium ([Ca2+]cyt) elevations. In contrast, high light and exogenous hydrogen peroxide (H2O2) induce large, sustained [Ca2+]str elevations that are not replicated in the cytosol. Measurements using the fluorescent H2O2 sensor roGFP2-Oxidant Receptor Peroxidase 1 (Orp1) indicate that [Ca2+]str elevations induced by these stimuli correspond to the accumulation of H2O2 in the chloroplast. [Ca2+]str elevations were also induced by adding methyl viologen, which generates superoxide within the chloroplast, and by treatments that disrupt nonphotochemical quenching (NPQ). The findings indicate that diatoms generate specific [Ca2+]str elevations in response to high light and oxidative stress that likely modulate the activity of calcium-sensitive components in photoprotection and other regulatory pathway