Air-Sea Exchange of Marine Trace Gases

Many of the reactive trace gases detected in the atmosphere are both emitted from and deposited to the global oceans via exchange across the air–sea interface. The resistance to transfer through both air and water phases is highly sensitive to physical drivers (waves, bubbles, films, etc.), which can either enhance or suppress the rate of diffusion. In addition to outlining the fundamental processes controlling the air–sea gas exchange, the authors discuss these drivers, describe the existing parameterizations used to predict transfer velocities, and summarize the novel techniques for measuring in situ exchange rates. They review trace gases that influence climate via radiative forcing (greenhouse gases), those that can alter the oxidative capacity of the atmosphere (nitrogen- and sulfur-containing gases), and those that impact ozone levels (organohalogens), both in the troposphere and stratosphere. They review the known biological and chemical routes of production and destruction within the water column for these gases, whether the ocean acts as a source or sink, and whether temporal and spatial variations in saturation anomalies are observed. A current estimate of the marine contribution to the total atmospheric flux of these gases, which often highlights the significance of the oceans in biogeochemical cycling of trace gases, is provided, and how air–sea gas fluxes may change in the future is briefly assessed.

Air-sea exchange of methanol and acetone during HiWinGS: Estimation of air phase, water phase gas transfer velocities

The air-sea fluxes of methanol and acetone were measured concurrently using a proton-transfer-reaction mass spectrometer (PTR-MS) with the eddy covariance (EC) technique during the High Wind Gas Exchange Study (HiWinGS) in 2013. The seawater concentrations of these compounds were also measured twice daily with the same PTR-MS coupled to a membrane inlet. Dissolved concentrations near the surface ranged from 7 to 28 nM for methanol and from 3 to 9 nM for acetone. Both gases were consistently transported from the atmosphere to the ocean as a result of their low sea surface saturations. The largest influxes were observed in regions of high atmospheric concentrations and strong winds (up to 25 m s(-1)). Comparison of the total air-sea transfer velocity of these two gases (K-a), along with the in situ sensible heat transfer rate, allows us to constrain the individual gas transfer velocity in the air phase (k(a)) and water phase (k(w)). Among existing parameterizations, the scaling of k(a) from the COARE model is the most consistent with our observations. The k(w) we estimated is comparable to the tangential (shear driven) transfer velocity previously determined from measurements of dimethyl sulfide. Lastly, we estimate the wet deposition of methanol and acetone in our study region and evaluate the lifetimes of these compounds in the surface ocean and lower atmosphere with respect to total (dry plus wet) atmospheric deposition.

Molecular mechanism of activation-triggered subunit exchange in Ca(2+)/calmodulin-dependent protein kinase II.

Activation triggers the exchange of subunits in Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), an oligomeric enzyme that is critical for learning, memory, and cardiac function. The mechanism by which subunit exchange occurs remains elusive. We show that the human CaMKII holoenzyme exists in dodecameric and tetradecameric forms, and that the calmodulin (CaM)-binding element of CaMKII can bind to the hub of the holoenzyme and destabilize it to release dimers. The structures of CaMKII from two distantly diverged organisms suggest that the CaM-binding element of activated CaMKII acts as a wedge by docking at intersubunit interfaces in the hub. This converts the hub into a spiral form that can release or gain CaMKII dimers. Our data reveal a three-way competition for the CaM-binding element, whereby phosphorylation biases it towards the hub interface, away from the kinase domain and calmodulin, thus unlocking the ability of activated CaMKII holoenzymes to exchange dimers with unactivated ones.

Molecular mechanism of activation-triggered subunit exchange in Ca(2+)/calmodulin-dependent protein kinase II.

Activation triggers the exchange of subunits in Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), an oligomeric enzyme that is critical for learning, memory, and cardiac function. The mechanism by which subunit exchange occurs remains elusive. We show that the human CaMKII holoenzyme exists in dodecameric and tetradecameric forms, and that the calmodulin (CaM)-binding element of CaMKII can bind to the hub of the holoenzyme and destabilize it to release dimers. The structures of CaMKII from two distantly diverged organisms suggest that the CaM-binding element of activated CaMKII acts as a wedge by docking at intersubunit interfaces in the hub. This converts the hub into a spiral form that can release or gain CaMKII dimers. Our data reveal a three-way competition for the CaM-binding element, whereby phosphorylation biases it towards the hub interface, away from the kinase domain and calmodulin, thus unlocking the ability of activated CaMKII holoenzymes to exchange dimers with unactivated ones.

Phaeocystis colony distribution in the North Atlantic Ocean since 1948, and interpretation of long-term changes in the Phaeocystis hotspot in the North Sea

Monitoring of Phaeocystis since 1948 during the Continuous Plankton Recorder survey indicates that over the last 5.5 decades the distribution of its colonies in the North Atlantic Ocean was not restricted to neritic waters: occurrence was also recorded in the open Atlantic regions sampled, most frequently in the spring. Apparently, environmental conditions in open ocean waters, also those far oVshore, are suitable for complete lifecycle development of colonies (the only stage recorded in the survey). In the North Sea the frequency of occurrence was also highest in spring. Its southeastern part was the Phaeocystis abundance hotspot of the whole area covered by the survey. Frequency was especially high before the 1960s and after the 1980s, i.e., in the periods when anthropogenic nutrient enrichment was relatively low. Changes in eutrophication have obviously not been a major cause of long-term Phaeocystis variation in the southeastern North Sea, where total phytoplankton biomass was related signiWcantly to river discharge. Evidence is presented for the suggestion that Phaeocystis abundance in the southern North Sea is to a large extent determined by the amount of Atlantic Ocean water Xushed in through the Dover Strait. Since Phaeocystis plays a key role in element Xuxes relevant to climate the results presented here have implications for biogeochemical models of cycling of carbon and sulphur. Sea-to-air exchange of CO2 and dimethyl sulphide (DMS) has been calculated on the basis of measurements during single-year cruises. The considerable annual variation in phytoplankton and in its Phaeocystis component reported here does not warrant extrapolation of such figures.

Air/sea DMS gas transfer in the North Atlantic: evidence for limited interfacial gas exchange at high wind speed

Shipboard measurements of eddy covariance dimethylsulfide (DMS) air–sea fluxes and seawater concentration were carried out in the North Atlantic bloom region in June/July 2011. Gas transfer coefficients (k660) show a linear dependence on mean horizontal wind speed at wind speeds up to 11 m s−1. At higher wind speeds the relationship between k660 and wind speed weakens. At high winds, measured DMS fluxes were lower than predicted based on the linear relationship between wind speed and interfacial stress extrapolated from low to intermediate wind speeds. In contrast, the transfer coefficient for sensible heat did not exhibit this effect. The apparent suppression of air–sea gas flux at higher wind speeds appears to be related to sea state, as determined from shipboard wave measurements. These observations are consistent with the idea that long waves suppress near-surface water-side turbulence, and decrease interfacial gas transfer. This effect may be more easily observed for DMS than for less soluble gases, such as CO2, because the air–sea exchange of DMS is controlled by interfacial rather than bubble-mediated gas transfer under high wind speed conditions.

Seasonality and interannual variability of the European Slope Current from 20 years of altimeter data compared with in situ measurements

The European Slope Current (SC) is a major section of the warm poleward flow from the Atlantic to the Arctic, which also moderates the exchange of heat, salt, nutrients and carbon between the deep ocean and the European shelf seas. The mean structure of the geostrophic flow, seasonality, interannual variability and long-term trend of SC are appraised with an unprecedented continuous 20-year satellite altimeter dataset. Comparisons with long term in situ data showed a maximum correlation of r2=0.51 between altimeter and Acoustic Doppler Current Profilers (ADCP), with similar results for drogued buoy data. Mean geostrophic currents were appraised more comprehensively than previous attempts, and the paths of 4 branches of the North Atlantic Current (NAC) and positions of 5 eddies in the region were derived quantitatively. A consistent seasonal cycle in the flow of the SC was found at all 8 sections along the European shelf slope, with maximum poleward flow in the winter and minimum in the summer. The seasonal difference in the altimetry current speed amounted to ~8-10 cm s-1 at the northern sections, but only ~5 cm s-1 on the Bay of Biscay slopes. This extended altimeter dataset indicates significant regional and seasonal variations, and has revealed new insights into the interannual variability of the SC. It is shown that there is a peak poleward flow at most positions along a ~2000 km stretch of the continental slope from Portugal to Scotland during 1995-1997, but this did not clearly relate to the extreme negative North Atlantic Oscillation (NAO) in the winter of 1995-1996. The speed of the SC exhibited a long term decreasing trend of ~1% per year. By contrast the NAC showed no significant trend over the 20-year period. Major changes in the NAC occurred three times, and these changes followed decreases in the NAO index.

Arctic Oceanography - Oceanography: Atmosphere-Ocean Exchange, Biogeochemistry & Physics

The Arctic Ocean is, on average, the shallowest of Earth’s oceans. Its vast continental shelf areas, which account for approximately half of the Arctic Ocean’s total area, are heavily influenced by the surrounding land masses through river run-off and coastal erosion. As a main area of deep water formation, the Arctic is one of the main «engines» of global ocean circulation, due to large freshwater inputs, it is also strongly stratified. The Arctic Ocean’s complex oceanographic configuration is tightly linked to the atmosphere, the land, and the cryosphere. The physical dynamics not only drive important climate and global circulation patterns, but also control biogeochemical cycles and ecosystem dynamics. Current changes in Arctic sea-ice thickness and distribution, air and water temperatures, and water column stability are resulting in measurable shifts in the properties and functioning of the ocean and its ecosystems. The Arctic Ocean is forecast to shift to a seasonally ice-free ocean resulting in changes to physical, chemical, and biological processes. These include the exchange of gases across the atmosphere-ocean interface, the wind-driven ciruclation and mixing regimes, light and nutrient availability for primary production, food web dynamics, and export of material to the deep ocean. In anticipation of these changes, extending our knowledge of the present Arctic oceanography and these complex changes has never been more urgent.