Search results for "Photic zone"

Diversity and distribution of marine heterotrophic bacteria from a large culture collection

2020

16 pages, 5 figures, 3 tables, supplementary information https://doi.org/10.1186/s12866-020-01884-7

Holocene millennial-scale productivity variations in the Sicily Channel (Mediterranean Sea)

2008

[1] The calcareous nannofossil assemblages of Ocean Drilling Program Hole 963D from the central Mediterranean Sea have been investigated to document oceanographic changes in surface waters. The studied site is located in an area sensitive to large-scale atmospheric and climatic systems and to high- and low-latitude climate connection. It is characterized by a high sedimentation rate (the achieved mean sampling resolution is <70 years) that allowed the Sicily Channel environmental changes to be examined in great detail over the last 12 ka BP. We focused on the species Florisphaera profunda that lives in the lower photic zone. Its distribution pattern shows repeated abundance fluctuations of …

Fine stratification of microbial communities through a metagenomic profile of the photic zone

2017

ABSTRACTMost marine metagenomic studies of the marine photic zone analyze only samples taken at one or two depths. However, when the water column is stratified, physicochemical parameters change dramatically over relatively short depth intervals. We sampled the photic water column every 15m depth at a single point of an off-shore Mediterranean site during a period of strong stratification (early autumn) to evaluate the effects of small depth increases on the microbiome. Using genomic assembly and metagenomic read recruitment, we found major shifts in the community structure over small variations of depth, with most microbes showing a distribution limited to layers approximately 30 meters th…

Conflicting coccolithophore and geochemical evidence for productivity levels in the Eastern Mediterranean sapropel S1

2011

Abstract The cyclic development of anoxic conditions in the eastern Mediterranean deep sea waters is one of the most fascinating research topics in paleoceanographic studies. In combination with bottom water stagnation, enhanced primary production is a common explanation for the deposition of organic-rich layers (sapropels). This is supported by extensive evidence from both geochemical and micropaleontological studies. The correspondence of recent sapropel layers with peaks of the lower photic zone coccolithophore species Florisphaera profunda has been interpreted as a proxy for the development of a deep chlorophyll maximum (DCM), due to the pycnocline/nutricline shallowing into the lower p…

HIGH-RESOLUTION PALAEONVIRONMENTAL RECONSTRUCTION OF ODP HOLE 963D (SICILY CHANNEL) DURING THE LAST DEGLACIATION BASED ON CALCAREOUS NANNOFOSSILS

2004

Abstract A palaeoenvironmental reconstruction of Ocean Drilling Program (ODP) Hole 963D (Sicily Channel) has been obtained on the basis of quantitative abundance fluctuations in the calcareous nannofossil assemblages. The studied hole is characterized by a very high sedimentary resolution and covers the last ca. 20 kyr. A new palaeoclimatic curve, based on the Gephyrocapsa muellerae/Upper Photic Zone (UPZ) group ratio, permitted the detection of the rapid climatic fluctuations that characterized the last deglaciation. Cold water masses occupied the Sicily Channel during the glacial period and the Younger Dryas, whereas they were generally warm during the Bolling–Allerod and the Holocene. An…

Spatial distribution of phytoplankton and picocyanobacteria in Lake Tanganyika in March and April 1998

2003

The spatial distribution of phytoplankton and picocyanobacteria was studied in Lake Tanganyika in relation to environmental factors. Sampling was conducted within three weeks during the wet season of 1998 when the water column stratification was most stable. The secchi depth varied between 11 and 16 m, except off the river Malagarasi (3 m). The depth of the euphotic zone was 33 to 56 m. Altogether, 218 phytoplankton taxa were identified. Their total biomass varied between 13 and 88 mg m−3 fresh weight. Picocyanobacteria were present at very high densities (104 to 6 × 10 5 cells ml−1). The influence of the river Malagarasi appeared to spread along the water surface because of the lower densi…

Early Paleocene Paleoceanography and Export Productivity in the Chicxulub Crater

2021

The Chicxulub impact caused a crash in productivity in the world''s oceans which contributed to the extinction of ~75% of marine species. In the immediate aftermath of the extinction, export productivity was locally highly variable, with some sites, including the Chicxulub crater, recording elevated export production. The long-term transition back to more stable export productivity regimes has been poorly documented. Here, we present elemental abundances, foraminifer and calcareous nannoplankton assemblage counts, total organic carbon, and bulk carbonate carbon isotope data from the Chicxulub crater to reconstruct changes in export productivity during the first 3 Myr of the Paleocene. We sh…

Seasonal variation of average phytoplankton concentration in the Kattegat—a periodical point model

2003

Abstract Seasonal variations in primary production, phytoplankton biomass, chlorophyll-a, dissolved inorganic phosphorus and nitrogen concentrations in the upper 10 m of the Kattegat were analysed by means of monitoring data from 1993–1997. Spatial optimal analysis, based on a stochastic model, was used to reconstruct weekly constituent fields onto a spatial grid. The reconstructed fields were spatially integrated, resulting in a relatively smooth seasonal variability of the average variables. A simple dynamical model, set up as a periodical boundary problem, is suggested for the average phytoplankton concentration, dissolved inorganic nitrogen and entrainment depth as state variables. The …

The “Alluvial Mesovoid Shallow Substratum”, a New Subterranean Habitat

2013

Received: April 5, 2013; Accepted: August 23, 2013; Published: October 4, 2013

2001

The main limnological characteristics of the biogenic meromictic Lake La Cruz, a small karstic lake located on a dolomitic substrate, are outlined below. The lake owes its chemical stratification mainly to high concentrations of bicarbonate and calcium in the permanent monimolimnion, located below a depth of 19 m. A massive precipitation of CaCO3 crystals ("whiting"), occurring in the euphotic zone every summer, leads to further sedimentation and redissolution in deep waters with enhanced CO2 concentrations. Other ions, like magnesium, ammonium, reduced iron, silicate, etc. also contribute to the chemically-induced stability of the monimolimnion. The patterns of stratification during two co…