Ichthyoplankton spatial distribution and its relation with water column stratification in fjords of southern Chile (46°48′–50°09′S) in austral spring 1996 and 2008

Abstract. The Baltic Sea, one of the world's largest brackish-marine basins, established after deglaciation of Scandinavia about 17 000 to 15 000 yr ago. In the changeable history of the Baltic Sea, the initial freshwater system was connected to the North Sea about 8000 yr ago and the modern brackish-marine setting (Littorina Sea) was established. Today, a relatively stable stratification has developed in the water column of the deep basins due to salinity differences. Stratification is only occasionally interrupted by mixing events, and it controls nutrient availability and growth of specifically adapted microorganisms and algae. We studied bacteriohopanepolyols (BHPs), lipids of specific bacterial groups, in a sediment core from the central Baltic Sea (Gotland Deep) and found considerable differences between the distinct stages of the Baltic Sea's history. Some individual BHP structures indicate contributions from as yet unknown redoxcline-specific bacteria (bacteriohopanetetrol isomer), methanotrophic bacteria (35-aminobacteriohopanetetrol), cyanobacteria (bacteriohopanetetrol cyclitol ether isomer) and from soil bacteria (adenosylhopane) through allochthonous input after the Littorina transgression, whereas the origin of other BHPs in the core has still to be identified. Notably high BHP abundances were observed in the deposits of the brackish-marine Littorina phase, particularly in laminated sediment layers. Because these sediments record periods of stable water column stratification, bacteria specifically adapted to these conditions may account for the high portions of BHPs. An additional and/or accompanying source may be nitrogen-fixing (cyano)bacteria, which is indicated by a positive correlation of BHP abundances with Corg and δ15N.

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Diatoms as a paleoproductivity proxy in the NW Iberian coastal upwelling system (NE Atlantic)

Biogeosciences ◽

10.5194/bg-14-1165-2017 ◽

2017 ◽

Vol 14 (5) ◽

pp. 1165-1179 ◽

Cited By ~ 8

Author(s):

Diana Zúñiga ◽

Celia Santos ◽

María Froján ◽

Emilia Salgueiro ◽

Marta M. Rufino ◽

...

Keyword(s):

Water Column ◽

Surface Sediment ◽

Sediment Trap ◽

Coastal Upwelling ◽

Late Summer ◽

Early Summer ◽

Marine Diatom ◽

Photic Zone ◽

Upwelling System ◽

Water Column Stratification

Abstract. The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 (±5.6) 106 valves m−2 d−1) represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom-derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Furthermore, Chaetoceros spp. dominate during spring–early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes.

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Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica

Ocean Science Discussions ◽

10.5194/osd-6-1477-2009 ◽

2009 ◽

Vol 6 (2) ◽

pp. 1477-1512 ◽

Cited By ~ 2

Author(s):

M. Vichi ◽

A. Coluccelli ◽

M. Ravaioli ◽

F. Giglio ◽

L. Langone ◽

...

Keyword(s):

Bottom Sediment ◽

Water Column ◽

Sediment Trap ◽

Biogeochemical Model ◽

Bacterial Respiration ◽

Deposition Flux ◽

Austral Spring ◽

Degradation Rates ◽

Biogenic Material ◽

Biogenic Fluxes

Abstract. Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175° E–74° S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990–2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces the observed magnitude of the biogenic fluxes, especially those found in the bottom sediment trap, but the peaks are markedly delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that the timing of the observed fluxes depends first and foremost on the timing of surface production and on a combination of size-distribution and quality of the autochtonous biogenic material. It is hypothesized that the bottom sediment trap collects material originated from the rapid sinking of freshly-produced particles and also from the previous year's production period.

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The response of water column and sedimentary environments to the advent of the Messinian salinity crisis: insights from an onshore deep-water section (Govone, NW Italy)

Geological Magazine ◽

10.1017/s0016756820000874 ◽

2020 ◽

pp. 1-17

Author(s):

Mathia Sabino ◽

Francesco Dela Pierre ◽

Marcello Natalicchio ◽

Daniel Birgel ◽

Susanne Gier ◽

...

Keyword(s):

Water Column ◽

Deep Water ◽

Bottom Layer ◽

Messinian Salinity Crisis ◽

Sedimentary Environments ◽

Water Column Stratification ◽

Stratigraphic Architecture ◽

Spatial Changes ◽

Oxygen Stable Isotope ◽

Nw Italy

Abstract During Messinian time, the Mediterranean underwent hydrological modifications culminating 5.97 Ma ago with the Messinian salinity crisis (MSC). Evaporite deposition and alleged annihilation of most marine eukaryotes were taken as evidence of the establishment of basin-wide hypersalinity followed by desiccation. However, the palaeoenvironmental conditions during the MSC are still a matter of debate, chiefly because most of its sedimentary record is buried below the abyssal plains of the present-day Mediterranean Sea. To shed light on environmental change at the advent and during the early phase of the MSC, we investigated the Govone section from the Piedmont Basin (NW Italy) using a multidisciplinary approach (organic geochemical, petrographic, and carbon and oxygen stable isotope analyses). The Govone section archives the onset of the crisis in a succession of organic-rich shales and dolomite-rich marls. The MSC part of the succession represents the deep-water equivalent of sulphate evaporites deposited at the basin margins during the first phase of the crisis. Our study reveals that the onset of the MSC was marked by the intensification of water-column stratification, rather than the establishment of widespread hypersaline conditions. A chemocline divided the water column into an oxygen-depleted, denser and more saline bottom layer and an oxygenated, upper seawater layer influenced by freshwater inflow. Vertical oscillations of the chemocline controlled the stratigraphic architecture of the sediments pertaining to the first stage of the MSC. Accordingly, temporal and spatial changes of water masses with different redox chemistries must be considered when interpreting the MSC event.

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Phytoplankton bloom phenomena in the North Atlantic Ocean and Arabian Sea

ICES Journal of Marine Science ◽

10.1093/icesjms/fsu241 ◽

2015 ◽

Vol 72 (6) ◽

pp. 2021-2028 ◽

Cited By ~ 5

Author(s):

John F. Marra ◽

Tommy D. Dickey ◽

Albert J. Plueddemann ◽

Robert A. Weller ◽

Christopher S. Kinkade ◽

...

Keyword(s):

Water Column ◽

Mixed Layer ◽

Arabian Sea ◽

Phytoplankton Bloom ◽

Mixed Layer Depth ◽

Ocean Dynamics ◽

Layer Depth ◽

Diurnal Variability ◽

Water Column Stratification ◽

Iceland Basin

Abstract We review bio-optical and physical data from three mooring experiments, the Marine Light–Mixed Layers programme in spring 1989 and 1991 in the Iceland Basin (59°N/21°W), and the Forced Upper Ocean Dynamics Experiment in the central Arabian Sea from October 1994 to 1995 (15.5°N/61.5°E). In the Iceland Basin, from mid-April to mid-June in 1989, chlorophyll-a concentrations are sensitive to small changes in stratification, with intermittent increases early in the record. The spring increase occurs after 20 May, coincident with persistent water column stratification. In 1991, the bloom occurs 2 weeks earlier than in 1989, with a background of strong short-term and diurnal variability in mixed layer depth and minimal horizontal advection. In the Arabian Sea, the mixing response to the northeast and southwest monsoons, plus the response to mesoscale eddies, produces four blooms over the annual cycle. The mixed layer depth in the Arabian Sea never exceeds the euphotic zone, allowing interactions between phytoplankton and grazer populations to become important. For all three mooring experiments, change in water column stratification is key in producing phytoplankton blooms.

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Freshwater discharges drive high levels of methylmercury in Arctic marine biota

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1505541112 ◽

2015 ◽

Vol 112 (38) ◽

pp. 11789-11794 ◽

Cited By ~ 66

Author(s):

Amina T. Schartup ◽

Prentiss H. Balcom ◽

Anne L. Soerensen ◽

Kathleen J. Gosnell ◽

Ryan S. D. Calder ◽

...

Keyword(s):

Water Column ◽

Marine Mammals ◽

River Mouth ◽

Ecological Impacts ◽

Trophic Levels ◽

Indigenous Populations ◽

Marine Biota ◽

Terrestrial Organic Matter ◽

Water Column Stratification ◽

Freshwater Inputs

Elevated levels of neurotoxic methylmercury in Arctic food-webs pose health risks for indigenous populations that consume large quantities of marine mammals and fish. Estuaries provide critical hunting and fishing territory for these populations, and, until recently, benthic sediment was thought to be the main methylmercury source for coastal fish. New hydroelectric developments are being proposed in many northern ecosystems, and the ecological impacts of this industry relative to accelerating climate changes are poorly characterized. Here we evaluate the competing impacts of climate-driven changes in northern ecosystems and reservoir flooding on methylmercury production and bioaccumulation through a case study of a stratified sub-Arctic estuarine fjord in Labrador, Canada. Methylmercury bioaccumulation in zooplankton is higher than in midlatitude ecosystems. Direct measurements and modeling show that currently the largest methylmercury source is production in oxic surface seawater. Water-column methylation is highest in stratified surface waters near the river mouth because of the stimulating effects of terrestrial organic matter on methylating microbes. We attribute enhanced biomagnification in plankton to a thin layer of marine snow widely observed in stratified systems that concentrates microbial methylation and multiple trophic levels of zooplankton in a vertically restricted zone. Large freshwater inputs and the extensive Arctic Ocean continental shelf mean these processes are likely widespread and will be enhanced by future increases in water-column stratification, exacerbating high biological methylmercury concentrations. Soil flooding experiments indicate that near-term changes expected from reservoir creation will increase methylmercury inputs to the estuary by 25–200%, overwhelming climate-driven changes over the next decade.

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