Effects of variable winds on biological productivity on continental shelves in coastal upwelling systems

The production and distribution of biological material in wind-driven coastal upwelling systems are of global importance, yet they remain poorly understood. Production is frequently presumed to be proportional to upwelling rate, yet high winds can lead to advective losses from continental shelves, where many species at higher trophic levels reside. An idealized mixed-layer conveyor (MLC) model of biological production from constant upwelling winds demonstrated previously that the amount of new production available to shelf species increased with upwelling at low winds, but declined at high winds [Botsford, L.W., Lawrence, C.A., Dever, E.P., Hastings, A., Largier, J., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259]. Here we analyze the response of this model to time-varying winds for parameter values and observed winds from the Wind Events and Shelf Transport (WEST) study region. We compare this response to the conventional view that the results of upwelling are proportional to upwelled volume. Most new production per volume upwelled available to shelf species occurs following rapid increases in shelf transit time due to decreases in wind (i.e. relaxations). However, on synoptic, event time-scales shelf production is positively correlated with upwelling rate. This is primarily due to the effect of synchronous periods of low values in these time series, paradoxically due to wind relaxations. On inter-annual time-scales, computing model production from wind forcing from 20 previous years shows that these synchronous periods of low values have little effect on correlations between upwelling and production. Comparison of model production from 20 years of wind data over a range of shelf widths shows that upwelling rate will predict biological production well only in locations where cross-shelf transit times are greater than the time required for phytoplankton or zooplankton production. For stronger mean winds (narrower shelves), annual production falls below the peak of constant wind prediction [Botsford et al., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259], then as winds increase further (shelves become narrower) production does not decline as steeply as the constant wind prediction.     

Atmospherically-promoted photosynthetic activity in a well-mixed ecosystem: Significance of wet deposition events of nitrogen compounds

Wet atmospheric deposition of dissolved N, P and Si species is studied in well-mixed coastal ecosystem to evaluate its potential to stimulate photosynthetic activities in nutrient-depleted conditions. Our results show that, during spring, seawater is greatly depleted in major nutrients: Dissolved Inorganic Nitrogen (DIN), Dissolved Inorganic Phosphorus (DIP) and Silicic acid (Si), in parallel with an increase of phytoplanktonic biomass. In spring (March–May) and summer (June–September), wet atmospheric deposition is the predominant source (>60%, relative to riverine contribution) for nitrates and ammonium inputs to this N-limited coastal ecosystem. During winter (October–February), riverine inputs of DIN predominate (>80%) and are annually the most important source of DIP (>90%). This situation allows us to calculate the possibility for a significant contribution to primary production in May 2003, from atmospheric deposition (total input for DIN ≈300 kg km⁻² month⁻¹). Based on usual Redfield ratios and assuming that all of the atmospheric-derived N (AD-N) in rainwater is bioavailable for phytoplankton growth, we can estimate new production due to AD-N of 950 mg C m⁻² month⁻¹, during this period of depletion in the water column. During the same episode (May 2003), photosynthetic activity rate, considered as gross primary production, was estimated to approximately 30 300 mg C m⁻² month⁻¹. Calculation indicates that new photosynthetic activity due to wet atmospheric inputs of nitrogen could be up to 3%.     

A climatology of mesoscale model simulated low-level wind jets over Cook Inlet and Shelikof Strait, Alaska

Weather in the North Gulf of Alaska is characterized by a high frequency of deep synoptic-scale low-pressure systems, especially during the cold season. The strong pressure gradients of these storms interact with the extremely rugged terrain of the coastal mountains to produce a variety of channeled flows. These surface wind regimes are not well documented in the scientific community, due to the paucity of observations. Modeling of these phenomena in regions of complex terrain is of great interest to those working with hydrodynamic, wave, and pollutant transport models in coastal and shelf areas. Such models, when coupled with ocean and coastal-ecology counterparts, give a broad view of the role surface winds play in shaping local coastal marine ecosystem in this region. This paper presents a climatology of simulated low-level wind jets over the domain of Cook Inlet and Shelikof Strait along Alaska's south-central coast. Daily simulations using the RAMS model were conducted in a 36-h forecast mode for the cold-season period 10/1/03 to 3/31/04. Systematic analysis of the resulting simulated low-level wind field makes it possible to characterize these jets and gap flows in spatial and temporal detail. The comparison between the RAMS winds and the Synthetic Aperture Radar (SAR)-derived winds when available verifies the existence of these wind jets and the capability of the model to simulate these cases. Clearly, the results of a study in this region depend on the fidelity of the model at these scales (O[5 km]). The SAR comparisons attempt to help establish this. From the 6 months of simulations over Cook Inlet and Shelikof Strait, the low-level wind jets are classified into 10 different regimes by location and orientation. These regimes are categorized into four more general groups: cross-channel westerly, easterly, and up and down Inlet flows. The nature of a particular regime is largely a function of pressure gradient orientation and local topography. Jets in the same group have a similar occurrence distribution with time. Some form of jet occurred in the study region almost daily each month of the period, with December 2003 having the highest frequency of wind jets.     

Holocene Faunal Trends in West Siberia and Their Causes

Based on an analysis of the transformation of vertebrate and invertebrate fauna of West Siberia in the Holocene, the classification and periodization of the main faunal trends are presented. Against the background of changing environmental conditions, the key regularities of the faunal dynamics, and the ways some species penetrate into the territory of the region and others disappear from the beginning of the Holocene to the present time have been indicated. Three global and four fluctuating trends are identified. The anthropogenic trend is ascertained separately. A conclusion is made about the prevailing causes of these changes, associated primarily with periodic climatic processes of different levels, determined by planetary geological and cosmic cycles. It is emphasized that, in the historical period, anthropogenic factors play a significant role in the regional faunal dynamics.     

Microbial activity promotes the enrichment of cobalt over nickel on hydrogenetic ferromanganese crusts

The different mineral phases of the ferromanganese (Fe–Mn) crusts stem from the interaction of biotic and abiotic components. It is therefore vital to study the activity of these components to decipher their contribution to the enrichment/depletion of metals in the crust. Thus, the present study examined sorption and release of Co and Ni by Fe-Mn crusts with associated microbial communities in the presence and absence of the metabolic poison sodium azide (15?mM). The study was conducted in the presence (G⁺) and absence (G^?) of added glucose (0.1%) at temperatures of 4?±?1°C and 28?±?2°C. Results showed that the microbial community had maximal sorption of Co of 66.12?µg?g^?1 at 4?±?1°C in the absence of added glucose and 479.75?µg?g^?1 at 28?±?2°C in the presence of added glucose. Maximum sorption of Ni in the absence of added glucose was 1.89?µg?g^?1 at 4?±?1°C and release of Ni was 51.28?µg?g^?1 in the presence of added glucose. Under abiotic conditions with 15?mM sodium azide as a metabolic inhibitor, significant amounts of Co and Ni were released in the G⁺ medium. Total cell counts on the Fe-Mn crust in the presence of added glucose increased by an order of magnitude from 10⁶ to 10⁷ cells g^?1 and in the absence of added glucose remained within the order of 10⁶ cells?g^?1 irrespective of temperature of incubation. Microscopic observation of the samples from biotic incubations showed numerous bacterial cells, exopolysaccharides, and structures resembling secondary minerals formed by bacteria. The results indicate that bacteria promote the enrichment of Co and Ni on the hydrogenetic Fe-Mn crusts by sorption processes and release of Ni by reductive dissolution of the oxides. The higher enrichment of Co than Ni is attributed to the way in which microbes interact with the metals.     

Philopatry and dispersal of juvenile leervis Lichia amia (Teleostei: Carangidae) tagged in a warm-temperate South African estuary

Understanding and characterising movement and area-use patterns of fishes within estuaries, as well as understanding the degree of connectivity between estuaries and the marine environment, can provide important insights into a species’ ecology, which is fundamental for effective management and conservation. Mark-and-recapture data obtained from the 082 TAG FISH Project, a dart-tagging programme, were used to describe movement patterns of juvenile leervis Lichia amia in the permanently open Swartkops Estuary, South Africa, as well as the degree of connectivity with the adjacent marine environment. A total of 628 juvenile leervis were tagged from 2008 to 2015, of which 77 fish (12.3%) were recaptured, with juveniles comprising 85.7% of all measured recaptures. The majority of recaptures (75.3%) were made within the Swartkops Estuary, indicating estuarine philopatry, with 23.4% having moved less than 1 km, revealing site fidelity, but most (51.9%) displaying estuarine roaming. A smaller portion of recaptures (27.7%) had dispersed to other habitats; 16 (20.8%) displayed multiple-habitat connectivity, while only 3 (3.9%) had undertaken long-distance movements (>100 km) and were recaptured up to 825 km northeast of the Swartkops Estuary. Lichia amia that had moved greater distances were characterised by a greater mean size and age at the time of recapture. This study provides valuable information on the philopatry and dispersal of juvenile L. amia.     

Peculiarities of slick formation on the sea surface

This paper deals with surface slicks, their nature, and causes of formation in context of the development of remote detection methods and investigation of dynamic processes in the ocean and at the air–ocean interface. A simplified formalism is introduced for slick–sea surface contrast formation which takes into account the upward sea radiation and qualitatively explains in situ measurement results. The results of a detection of slicks on the coastal water surface are also described, which, together with the simplified formalism suggested, provide optimal experimental conditions for slick–sea surface contrast measurements; i.e., the contrast of the P component of reflected radiation is measured at viewing angles close to the horizon.     

Features of Manifestation of the Chilean Tsunami on April 1, 2014, and September 16, 2015, on Russia’s Pacific Coast

As a result of mooring of autonomous seabed stations in bays of Shikotan Island, the records of two tsunamis were obtained from strong earthquakes that occurred off the coast of Chile on April 1, 2014, and September 16, 2015. In both cases, prolonged intense vibrations with a pronounced group structure were observed in various bays, mainly with periods of the main modes of resonance oscillations. The second event was more dangerous, and the wave height was 0.9 m at Malokurilskaya Bay. The increase in the energy of fluctuations in 2015 was more significant, manifesting itself in a wider range of periods. Numerical simulation of the tsunami showed that the nature of wave propagation in both earthquakes was identical in the northern part of the Pacific Ocean, approaching Russia’s Pacific coast, and was characterized by weak damping, in contrast to waves propagating to the south and southwest. This explains why expect large waves can be expected on the coasts of the Kurils from earthquakes off the coast of South America, despite the considerable distance.     

Characterisation and preliminary quantification of the methane reservoir in a coastal sedimentary source: San Simón Bay,Ría de Vigo,NW Spain

Ría de Vigo is a river valley flooded by the sea, with a bay (San Simón Bay) at its innermost part. The accumulation of Holocene sediment in San Simón Bay has been studied by the integration of 1) large scale high resolution seismic data, and 2) detailed geochemical analysis of a gravity core. In San Simón Bay the majority of the seismic records are obscured by acoustic turbidity which represents gassy sediments, but on records from Rande Strait it is possible to distinguish two Quaternary seismic sequences; an Upper Pleistocene sequence (SQ1) and a Holocene sequence (SQ2). Only SQ2 is recognized in San Simón Bay where it is comprised of two seismic units; the upper unit represents the HST sediment, i.e. the period of highest sea level. A gravity core taken within the gassy zone at 10 m water depth provided 3.55 m of fine-grained sediments (muds) from the youngest seismic unit (4 m thick). Geochemical analysis show high values (4 to 10%) of TOC. Sediment and porewater analyses indicate a distinct sulphate–methane transition zone (SMTZ) between 60 and 80 cm where sulphate is depleted (to <1.7 mM) and methane increases (to >0.4 mM). The top of the acoustic turbidity (the gas front) at 80 cm corresponds to the lower limit of the SMTZ. The methane cannot have been derived from the underlying metamorphic and granitic rocks, but was probably derived by microbial degradation of the organic matter in the Holocene sediments. We estimate that the sediments of the Bay contain approximately 1.8 × 10⁶ m³ of organic carbon and 275 ton of methane.     

Burial and degradation of organic carbon in Louisiana shelf/slope sediments

The primary focus of this paper is to better understand carbon burial on the Louisiana continental margin using spatial scales that covered various shelf depositional areas far-field and near-field (sediment and organic carbon inputs relative to river mouth proximity) and covering a variety of sedimentation rates. Box-cores samples were collected in July 2003; cores were collected along two depositional transects extending westward and southward from the Southwest Pass (SW Pass). A key difference between the two transects sampled in this study was the greater occurrence of mobile muds derived from spillover from shallower regions along the westward 50 m isobaths. The dominant mechanism for mixing in the surface active zone (SAZ) on the inner Louisiana shelf was due to physical, not biological, forces. Burial efficiencies for organic carbon (57.2–91.5%) and total nitrogen (44.2–86.9%) ranged widely across all shelf stations. Lower burial efficiencies for bulk organic carbon, total nitrogen, and pigment biomarkers were associated with mobile muds west of Southwest Pass. Chlorophyll a concentrations were significantly higher than pheopigments at depth at the Mississippi River and Southwest Pass stations, making up 40.4 and 77.4% of total pigment concentrations in the (SAZ) and 46.2 and 63.2% in the accumulation zone (AZ), respectively. These results are in agreement with earlier plant pigment studies which showed that a large fraction of the phytodetritus delivered to the inner shelf was derived from coastal and river diatoms. The amount of lignin preserved with depth decreased with increasing residence time in the SAZ and diagenetic zone (DZ) along the canyon transect but not along the western transect. Trends for lignin concentration followed previously identified surface sediment trends indicating overall lower burial of refractory terrestrial material at depth with greater distance offshore.