Posts Tagged 'Arctic'



Freshening of the western Arctic negates anthropogenic carbon uptake potential

As human activities increase the atmospheric concentration of carbon dioxide (CO2), the oceans are known to absorb a significant portion. The Arctic Ocean has long been considered to have enormous potential to sequester anthropogenic CO2, and mitigate emissions. The frigid waters make CO2 more soluble, and as sea ice melts, greater surface area is exposed to absorb CO2. However, sparse data have made quantifying the amount of anthropogenic CO2 in the Arctic difficult, stimulating much debate over the basin’s contribution to CO2 sequestration from the atmosphere. Using three separate cruises in 1994, 2005, and 2015 in the Canada and Makarov basins, we analyze the decadal variability in anthropogenic CO2 uptake in the central western Arctic. Here we show, from direct carbon system measurements spanning two decades, that despite increased atmospheric CO2, total dissolved inorganic carbon has actually decreased, with minimal anthropogenic CO2 uptake. The reduction in dissolved CO2 results from a dilution of total alkalinity by increased freshwater supply, particularly river water. Changes in the freshwater budget of the western Arctic override its uptake potential, resulting in a weak sink, or possibly source of CO2.

Continue reading ‘Freshening of the western Arctic negates anthropogenic carbon uptake potential’

The recent state and variability of the carbonate system of the Canadian Arctic in the context of ocean acidification

Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecosystems around the globe. The Arctic Ocean is particularly vulnerable to acidification due to its relatively low buffering capacity and, thus, is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the carbonate mineral aragonite (ΩA < 1), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago. Nonetheless, few of these observations were made in the last five years and the spatial coverage in the latter region is poor. Additionally, the strong variability inherent to this dynamic shelf environment renders the temporal imprint of ocean acidification on carbonate system parameters (pH, pCO2, DIC, Ω) virtually indistinguishable on decadal timescales. We use a dataset of carbonate system parameters measured in Canadian Arctic Archipelago (CAA) and its adjacent basins to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability. Our findings reveal that, in addition to the surface of the Canada Basin, the entire water column of the Queen Maud Gulf was undersaturated with respect to aragonite in 2015 and 2016. We also estimate that approximately a third of the interannual variability in surface DIC in the CAA results from fluctuations in biological activity.

Continue reading ‘The recent state and variability of the carbonate system of the Canadian Arctic in the context of ocean acidification’

Origin and accumulation of an anthropogenic CO2 and 13C Suess effect in the Arctic Ocean

We determined the impact of anthropogenic CO2 (Cant) accumulation on the δ13C of dissolved inorganic carbon (DIC) in the Arctic Ocean (i.e., the 13C Suess effect) based on δ13C measurements during a GEOTRACES cruise in 2015. The δ13C decrease was estimated from the amount of Cant change derived by the transit time distribution (TTD) approach and the ratio of the anthropogenic δ13C/DIC change (RC). A significant Cant increase (up to 45 μmol kg−1) and δ13C decrease (up to −0.9‰) extends to ~2000 m in the Canada and Makarov Basin. We find distinctly different RC values for the intermediate water (300–2000 m) and upper halocline water (<200 m) of −0.020 and −0.012‰ (μmol kg−1)−1, respectively, which identifies two sources of Cant accumulation from North Atlantic and North Pacific. Furthermore, estimated RC for intermediate waters is the same as the RC observed in the Greenland Sea and the rate of anthropogenic DIC increase estimated for intermediate waters at 0.9 μmol kg−1 yr−1 is identical to the estimated rate in the Iceland Sea. These observations indicate that the high rate of Cant accumulation and δ13C decrease in the Arctic Ocean is primarily a result of the input of Cant, via ventilation of intermediate waters, from the Nordic Sea rather than local anthropogenic CO2 uptake within the Arctic Basin. We determine the preindustrial δ13C (δ13CPI) distributions and find distinct δ13CPI signatures of the intermediate and upper halocline waters that reflect the difference in δ13CPI–PO4 relationship of Atlantic and Pacific source water.

Continue reading ‘Origin and accumulation of an anthropogenic CO2 and 13C Suess effect in the Arctic Ocean’

Impact of climate change and ocean acidification on ocean-based industries and society in Norway

This report presents a review of the scientific literature on how key ecosystems, ecosystem services and ocean-based industries in Norway are affected by climate change and ocean acidification today and under future scenarios. The project has also compiled knowledge on how ocean-based actions can help mitigate and reduce the magnitude of climate change, ocean acidification and environmental problems. Further possible trade-off related to ocean-based action were identified as well as how climate change and ocean acidification may potentially affect these ocean-based opportunities. Finally, the report presents published findings on possible future impacts on society and implications for policy and management.

Continue reading ‘Impact of climate change and ocean acidification on ocean-based industries and society in Norway’

The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)

Compared to the rest of the globe, the Arctic Ocean is affected disproportionately by climate change. Despite these fast environmental changes, we currently know little about the effects of ocean acidification (OA) on marine key species in this area. Moreover, the existing studies typically test the effects of OA under constant, hence artificial, light fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to current (400 µatm) and future (1000 µatm) pCO2 levels under a constant as well as a dynamic light, simulating more realistic light fields as experienced in the upper mixed layer. To describe and understand the responses to these drivers, growth, particulate organic carbon (POC) production, elemental composition, photophysiology and reactive oxygen species (ROS) production were analysed. M. pusilla was able to benefit from OA on various scales, ranging from an increase in growth rates to enhanced photosynthetic capacity, irrespective of the light regime. These beneficial effects were, however, not reflected in the POC production rates, which can be explained by energy partitioning towards cell division rather than biomass build-up. In the dynamic light regime, M. pusilla was able to optimize its photophysiology for effective light usage during both low- and high-light periods. This photoacclimative response, which was achieved by modifications to photosystem II (PSII), imposed high metabolic costs leading to a reduction in growth and POC production rates when compared to constant light. There were no significant interactions observed between dynamic light and OA, indicating that M. pusilla is able to maintain effective photoacclimation without increased photoinactivation under high pCO2. Based on these findings, M. pusilla is likely to cope well with future conditions in the Arctic Ocean.

Continue reading ‘The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)’

Impacts of temperature, CO2, and salinity on phytoplankton community composition in the western Arctic Ocean

The Arctic Ocean has been experiencing rapid warming, which accelerates sea ice melt. Further, the increasing area and duration of sea ice-free conditions enhance ocean uptake of CO2. We conducted two shipboard experiments in September 2015 and 2016 to examine the effects of temperature, CO2, and salinity on phytoplankton dynamics to better understand the impacts of rapid environmental changes on the Arctic ecosystem. Two temperature conditions (control: <3 and 5°C above the control), two CO2 levels (control: ∼300 and 300/450 μatm above the control; i.e., 600/750 μatm), and two salinity conditions (control: 29 in 2015 and 27 in 2016, and 1.4 below the control) conditions were fully factorially manipulated in eight treatments. Higher temperatures enhanced almost all phytoplankton traits in both experiments in terms of chl-a, accessory pigments and diatom biomass. The diatom diversity index decreased due to the replacement of chain-forming Thalassiosira spp. by solitary Cylindrotheca closterium or Pseudo-nitzschia spp. under higher temperature and lower salinity in combination. Higher CO2 levels significantly increased the growth of small-sized phytoplankton (<10 μm) in both years. Decreased salinity had marginal effects but significantly increased the growth of small-sized phytoplankton under higher CO2 levels in terms of chl-a in 2015. Our results suggest that the smaller phytoplankton tend to dominate in the shelf edge region of the Chukchi Sea in the western Arctic Ocean under multiple environmental perturbations.

Continue reading ‘Impacts of temperature, CO2, and salinity on phytoplankton community composition in the western Arctic Ocean’

Coastal acidification induced by biogeochemical processes driven by sea-ice melt in the western Arctic Ocean

To better understand the extent of acidification in the Arctic Ocean, we present pH measurements collected along a shelf-slope-basin transect from the Chukchi Sea shelf to the Chukchi Abyssal Plain (CAP) in the western Arctic Ocean during the summer 2010 Chinese Arctic National Research Expedition (CHINARE) cruise. We observed low pH values in the Chukchi Sea shelf bottom waters (∼30 m-bottom) and CAP upper haloline layer (UHL) (100-200 m). In the shelf bottom waters, the pH values were 7.66-8.13, about 0.07-0.68 pH units lower than the surface values of 8.20-8.24. In the CAP subsurface waters, the pH values were 7.85-7.98, about 0.08-0.31 pH units lower than the surface values of 8.20-8.24. Biogeochemical model simulations suggest that remineralized CO2 driven by sea-ice loss is primarily responsible for the low pH values in the bottom waters of the Chukchi Sea (shelf) and the UHL waters of the CAP (basin). Recent sea-ice melt enhanced organic matter production in surface waters and subsequent supported the increased microbial respiration of organic matter in bottom waters. Moreover, low pH bottom waters were flushed into the UHL during winter to sustain the low pH characteristics in the subsurface basin layers. In addition, our simplified model suggests that the thermodynamic effect of pH on is small. However, increasing temperature significantly increased aragonite saturation (Ωarag) which slowed down the speed of acidification.

Continue reading ‘Coastal acidification induced by biogeochemical processes driven by sea-ice melt in the western Arctic Ocean’

Dense Mytilus beds along freshwater-influenced Greenland shores: resistance to corrosive waters under high food supply

Arctic calcifiers are believed to be particularly vulnerable to ocean acidification as the Arctic already experiences low carbonate saturations states due to low temperature and high inputs of freshwater. Here, we report the finding of dense beds of Mytilus growing in tidal lagoons and river mouths, where the availability of carbonate ions is remarkably low Ωarag < 0.5. Although these Mytilus grow in the intertidal zone, and therefore are covered by seawater during high tide, δ18O isotopes of shell carbonate were low − 2.48 ± 0.05‰, confirming that their shells were deposited under low salinity conditions, i.e., reflecting a contribution from 18O-depleted freshwater. δ18O isotopes of shell carbonate became heavier with increasing salinity, with mean values of − 0.74 ± 0.96‰ for Mytilus growing in tidal pools. We calculated, based on δ18O isotopic composition standardized to a common temperature, that freshwater accounted for 7% of the carbonate oxygen in the shells of Mytilus at the habitats with near full-strength seawater salinity compared with 25% in shells collected at sites temporarily exposed to freshwater. The composition of the periostracum revealed a trend for shells from river mouths and brackish tidal lagoons to be more depleted in polysaccharides than shells exposed to higher salinity. We conclude that the high food supply associated with riverine discharge allows Mytilus to cope with the low saturation states by using energy to calcify and modify their periostracum to protect the shells from dissolution. These findings suggest that Arctic Mytilus are highly resistant to low saturation states of carbon minerals if supplied with sufficient food.

Continue reading ‘Dense Mytilus beds along freshwater-influenced Greenland shores: resistance to corrosive waters under high food supply’

Two decades of ocean acidification in the surface waters of the Beaufort Gyre, Arctic Ocean: effects of sea ice melt and retreat from 1997‐2016

Anthropogenic CO2 uptake drives ocean acidification and so decreases the calcium carbonate (CaCO3) saturation state (Ω). Undersaturation of surface water with respect to aragonite‐type CaCO3 was first reported for 2008 in the Canada Basin, preceding other open ocean basins. This study reveals interannual variation of Ω in the surface Canada Basin before and after 2008. A rapid decrease of Ω occurred during 2003‐2007 at a rate of ‐0.09 yr‐1, 10 times faster than other open oceans. This was due to melting and retreat of sea ice, which diluted surface water and enhanced air‐sea CO2 exchange. After 2007, Ω did not further decrease, despite increasing atmospheric CO2 and continued sea ice retreat. A weakened dilution effect from sea‐ice melt and stabilized air‐sea CO2 disequilibrium state are the main reasons for this stabilization of Ω. Aragonite undersaturation has been observed for the last 11 years and aragonite shelled organisms may be threatened.

Continue reading ‘Two decades of ocean acidification in the surface waters of the Beaufort Gyre, Arctic Ocean: effects of sea ice melt and retreat from 1997‐2016’

A meta-analysis of microcosm experiments shows that dimethyl sulfide (DMS) production in polar waters is insensitive to ocean acidification

Emissions of dimethylsulfide (DMS) from the polar oceans play a key role in atmospheric processes and climate. Therefore, it is important to increase our understanding of how DMS production in these regions may respond to climate change. The polar oceans are particularly vulnerable to ocean acidification (OA). However, our understanding of the polar DMS response is limited to two studies conducted in Arctic waters, where in both cases DMS concentrations decreased with increasing acidity. Here, we report on our findings from seven summertime shipboard microcosm experiments undertaken in a variety of locations in the Arctic Ocean and Southern Ocean. These experiments reveal no significant effects of short-term OA on the net production of DMS by planktonic communities. This is in contrast to similar experiments from temperate north-western European shelf waters where surface ocean communities responded to OA with significant increases in dissolved DMS concentrations. A meta-analysis of the findings from both temperate and polar waters (n=18 experiments) reveals clear regional differences in the DMS response to OA. Based on our findings, we hypothesize that the differences in DMS response between temperate and polar waters reflect the natural variability in carbonate chemistry to which the respective communities of each region may already be adapted. If so, future temperate oceans could be more sensitive to OA, resulting in an increase in DMS emissions to the atmosphere, whilst perhaps surprisingly DMS emissions from the polar oceans may remain relatively unchanged. By demonstrating that DMS emissions from geographically distinct regions may vary in their response to OA, our results may facilitate a better understanding of Earth’s future climate. Our study suggests that the way in which processes that generate DMS respond to OA may be regionally distinct, and this should be taken into account in predicting future DMS emissions and their influence on Earth’s climate.

Continue reading ‘A meta-analysis of microcosm experiments shows that dimethyl sulfide (DMS) production in polar waters is insensitive to ocean acidification’


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Ocean acidification in the IPCC AR5 WG II

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