Exploring Ocean Biogeochemistry Using a Lab-on-Chip Phosphate Analyser on an Underwater Glider

The ability to make measurements of phosphate (PO43–) concentrations at temporal and spatial scales beyond those offered by shipboard observations offers new opportunities for investigations of the marine phosphorus cycle. We here report the first in situ PO43– dataset from an underwater glider (Kongsberg Seaglider) equipped with a PO43– Lab-on-Chip (LoC) analyser. Over 44 days, a 120 km transect was conducted in the northern North Sea during late summer (August and September). Surface depletion of PO43– (<0.2 μM) was observed above a seasonal thermocline, with elevated, but variable concentrations within the bottom layer (0.30–0.65 μM). Part of the variability in the bottom layer is attributed to the regional circulation and across shelf exchange, with the highest PO43– concentrations being associated with elevated salinities in northernmost regions, consistent with nutrient rich North Atlantic water intruding onto the shelf. Our study represents a significant step forward in autonomous underwater vehicle sensor capabilities and presents new capability to extend research into the marine phosphorous cycle and, when combined with other recent LoC developments, nutrient stoichiometry.

Offshore Wind Energy and the Mid-Atlantic Cold Pool: A Review of Potential Interactions

The U.S. East Coast has 1.7 million acres of federal bottom under lease for the development of wind energy installations, with plans for more than 1,500 foundations to be placed. The scale of these wind farms has the potential to alter the unique and delicate oceanographic conditions along the expansive Atlantic continental shelf, a region characterized by a strong seasonal thermocline that overlies cold bottom water, known as the “Cold Pool.” Strong seasonal stratification traps cold (typically less than 10°C) water above the ocean bottom sustaining a boreal fauna that represents vast fisheries, including the most lucrative shellfish fisheries in the United States. This paper reviews the existing literature and research pertaining to the ways in which offshore wind farms may alter processes that establish, maintain, and degrade stratification associated with the Cold Pool through vertical mixing in this seasonally dynamic system. Changes in stratification could have important consequences in Cold Pool setup and degradation, processes fundamental to high fishery productivity of the region. The potential for these multiple wind energy arrays to alter oceanographic processes and the biological systems that rely on them is possible; however, a great deal of uncertainty remains about the nature and scale of these interactions. Research should be prioritized that identifies stratification thresholds of influence, below which turbines and wind farm arrays may alter oceanographic processes. These should be examined within context of spatial and seasonal dynamics of the Cold Pool and offshore wind lease areas to identify potential areas of further study.

Environmental impacts of physical and dynamical characteristics of the southern coastal waters of the Caspian Sea

ABSTRACT This research evaluated the variability of current characteristics and seawater properties in the middle part of the southern shelf of the Caspian Sea. The effect of the coastal flow on marine debris dispreading was assessed in the southern Caspian Sea for the first time. The findings showed the existence of thermal stratification containing seasonal thermocline with thickness of about 40 m in the water column. Maximum monthly along-shore current velocities around 1.3 m s−1 were observed in November and December. Monthly variations were clearly found in both flow velocity and local wind components. However, no significant levels of correlation between wind and current speeds were observed during the study in the region. In some cases, the mean monthly cross-shore component velocities were measured at about 29 cm s−1 in November. The findings indicated that there was no upwelling phenomenon associated to the regional wind in the study area. In situ current measurements indicated dominant east and north-northeast directions, presumably related to the effect of general circulation in the southern basin. Current profiles in the water column displayed similarity in directions at 10, 15 and 20 m depths over the continental shelf. The field samples and analysis revealed that the soft and smaller-scale seawater litters can be carried long distances by the current along the coast. Most coastal based and marine litters originated from the tourist activities (in the middle and western parts of the shores) and waste emanated from the river (Tonekabon-Nowshahr).

Influence of the Seasonal Thermocline on the Vertical Distribution of Larval Fish Assemblages Associated with Atlantic Bluefin Tuna Spawning Grounds

Temperature is often an important variable influencing the vertical position of fish larvae in the water column. The same species may show different vertical distributions in areas with a strong near-surface seasonal thermocline compared to isothermal near-surface regions. In areas with a strong surface thermocline, tuna larvae show a significant preference for the near-surface warmer layers. Little is known regarding larval tuna vertical distribution in isothermal waters and on the vertical distribution of the associated larval fish assemblages. We conducted vertical stratified sampling using the same methodology and fishing device (MOCNESS) in the two major spawning areas of Atlantic bluefin tuna (BFT): western Mediterranean Sea (MED), characterized by a surface thermocline, and the Gulf of Mexico (GOM) which lacks thermal stratification. Tuna larvae occupied the upper 30 m in both areas, but the average larval depth distribution was consistently deeper in the GOM. In the MED, vertical distribution of larval fish assemblages was explained by temperature, and species such as BFT, Thunnus alalunga, and Ceratoscopelus maderensis, among others, coexist above the thermocline and are separated from species such as Cyclothone braueri and Hygophum spp. (found below the thermocline). In the GOM, the environmental correlates of the vertical distribution of the larvae were salinity and fluorescence. Mesopelagic taxa such as Ceratoscopelus spp. and Cyclothone spp., among others, had a shallower average distribution than Lampanyctus spp., Hygophum spp., and Myctophum spp.

Water exchange between the inner and outer archipelago areas of the Finnish Archipelago Sea in the Baltic Sea

We studied the water age and transport of passive tracers in the Archipelago Sea, Baltic Sea, using the COHERENS 3D hydrodynamic model and the OpenDrift Lagrangian particle model. The mean water age, which was calculated with COHERENS over a period of 6 years, varied between 1 and 3 months in the outer archipelago and between 3 and 6 months in the middle archipelago. The water age was highest in the inner archipelago, up to 7 months. As the density stratification is weak in large parts of this area, except for the seasonal thermocline, significant differences in the water age between the surface and bottom layers were seen only in the river mouths and in the deep channels of the middle archipelago. The Lagrangian particle simulations showed that the middle archipelago is more open towards the north than south. From the northern boundary, the Bothnian Sea, the largest transport to the middle archipelago occurred with NW winds. Due to the geometry and density of the islands in the area, the prevailing wind direction, SW, alone is not optimal for transporting tracer particles to the middle archipelago. From the southern boundary, the Baltic Proper, transport to the middle archipelago occurred mainly with SE winds and during events when the wind direction shifted from SW to SE or vice versa. The transport further into the inner archipelago was limited to only a few cases, indicating that the inner archipelago is fairly sheltered from transport from the outer archipelago.

Dispersion in the Open Ocean Seasonal Pycnocline at Scales of 1–10 km and 1–6 days

Results are presented from two dye release experiments conducted in the seasonal thermocline of the Sargasso Sea, one in a region of low horizontal strain rate (~10−6 s−1), the second in a region of intermediate horizontal strain rate (~10−5 s−1). Both experiments lasted ~6 days, covering spatial scales of 1–10 and 1–50 km for the low and intermediate strain rate regimes, respectively. Diapycnal diffusivities estimated from the two experiments were κz = (2–5) × 10−6 m2 s−1, while isopycnal diffusivities were κH = (0.2–3) m2 s−1, with the range in κH being less a reflection of site-to-site variability, and more due to uncertainties in the background strain rate acting on the patch combined with uncertain time dependence. The Site I (low strain) experiment exhibited minimal stretching, elongating to approximately 10 km over 6 days while maintaining a width of ~5 km, and with a notable vertical tilt in the meridional direction. By contrast, the Site II (intermediate strain) experiment exhibited significant stretching, elongating to more than 50 km in length and advecting more than 150 km while still maintaining a width of order 3–5 km. Early surveys from both experiments showed patchy distributions indicative of small-scale stirring at scales of order a few hundred meters. Later surveys show relatively smooth, coherent distributions with only occasional patchiness, suggestive of a diffusive rather than stirring process at the scales of the now larger patches. Together the two experiments provide important clues as to the rates and underlying processes driving diapycnal and isopycnal mixing at these scales.

Spatial distribution pattern of European hake, Merluccius merluccius (Pisces: Merlucciidae), in the Mediterranean Sea

The present study provides updated information on the occurrence, abundance and biomass distribution patterns and length frequencies of Merluccius merluccius in the Mediterranean Sea, by analysing a time series of data from the Mediterranean International Trawl Surveys (MEDITS) from 1994 to 2015. The highest values of abundance and biomass were observed in the Sardinian Seas. The use of a generalized additive model, in which standardized biomass indices (kg km–2) were analysed as a function of environmental variables, explained how ecological factors could affect the spatio-temporal distribution of European hake biomass in the basin. High biomass levels predicted by the model were observed especially at 200 m depth and between 14°C and 18°C, highlighting the preference of the species for colder waters. A strong reduction of biomass was observed since the year 2009, probably due to the strengthening of the seasonal thermocline that had greatly reduced the availability of food. The general decrease in biomass of several stocks of anchovy and sardine, preys of European hake, might be indirectly connected to the decreasing biomass detected in the present study. The length analysis shows median values lower than 200 mm total length of most of the investigated areas.

Properties of main phytoplankton species of the Black Sea, determining the change in their dominance in annual dynamics

Using mathematical model, we tested three hypotheses of bloom regulation mechanisms for dominant phytoplankton species in the northeastern Black Sea. The model is based on the concept of intracellular regulation using the Droop equation, and values of the model constants that satisfy the conditions of domination are found. The bloom of the small-cell diatom Pseudo-nitzschia pseudodelicatissima is due to higher specific growth rates than other species in early spring. The half-saturation constants and minimum quotas for mineral nutrition elements (nitrogen and phosphorus) are also relatively high. In late spring and early summer, the bloom of coccolithophore Emiliania huxleyi is usually recorded. Prerequisites are a low half-saturation constant for nitrogen uptake and minimum quota for this nutrient. The third mechanism gains strength in the summer with the deepening of seasonal thermocline and the dominance of large-cell diatoms. It was shown that for the supremacy of large diatom Proboscia alata, it is necessary to have low half-saturation constants for the phosphorus uptake and minimum quotas for this nutrient.