Organic-matter production and preservation and evolution of anoxia in the Holocene Black Sea

M.A. Arthur; W.E. Dean

doi:10.1029/98pa01161

Home/Archive/USGS

USGS · 70020235

Organic-matter production and preservation and evolution of anoxia in the Holocene Black Sea

M.A. Arthur·W.E. Dean

View original source ↗Export metadata ↓

Abstract

Dating of sediments collected in gravity cores during Leg 1 of the 1988 R/V Knorr expedition to the Black Sea suggests that the onset of water-column anoxia at ∼7.5 ka was virtually synchronous across the basin over a depth range of ∼200–2250 m. A finely laminated, organic carbon (OC) rich sapropel (unit II) was produced as a result of this anoxia. The trigger for increased OC production and development of anoxia was the spillover of saline waters through the Bosporus that probably began at ∼9.0 ka and peaked between ∼7.0 and 5.5 ka. This spillover enhanced vertical mixing and nutrient cycling and caused a short-term (2–3 kyr) burst in surface-water productivity during the early part of unit II deposition. Continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters, thus limiting primary production and decreasing the OC flux to sediments beginning ∼5.5 ka. Concentration, accumulation rate, and degree of preservation of organic matter all decreased in the upper part of unit II as a result of decreasing productivity, but anoxia persisted throughout most of the water column. The end of unit II sapropel deposition was synchronous across the Black Sea as the result of the first blooms of the coccolith Emiliania huxleyi , which presumably marked an increase in surface-water salinity above 11 and the beginning of unit I deposition. The high coccolith-carbonate fluxes that occurred during deposition of unit I diluted the OC concentration in the sediments, but OC accumulation rates are about the same as those in upper part of unit II.

Explore related subjects

Paleoceanography and Paleoclimatology Article

Source-reported bounding extent: 40.650546573165° to 47.20293053871663° latitude; 26.631280052971448° to 42.86799025318777° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

M.A. Arthur, W.E. Dean. 2010-05-04. Organic-matter production and preservation and evolution of anoxia in the Holocene Black Sea. https://doi.org/10.1029/98pa01161

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

On the fidelity of oxygen isotope-based sea level reconstructions: A case study of Marine Isotope Stage 3

Although foraminiferal oxygen isotope records (δ 18 O F ) have long been used to develop time-continuous estimates of past global ice volume, growing evidence indicates that the ice volume and temperature contributions to δ 18 O F diverge considerably over the last glacial cycle. Across Marine Isotope Stage 3 (MIS 3; 57 to 29 ka), estimates of peak global sea level based on δ 18 O F are ∼30 m lower than reconstructions based on recent glacial geology, geologic sea-level records, and glacial isostatic adjustment (GIA) modeling approaches. Here we address this mismatch by quantifying uncertainties in converting δ 18 O F to global sea level during MIS 3. We review the geochemical tools to assess the contributions of ocean temperature, diagenesis, and the isotopic composition of ice sheets to δ 18 O F records across MIS 3. We show that recent advances in our understanding of these and other factors that contribute uncertainty (e.g., global sea level during the Last Glacial Maximum) help to explain the MIS 3 gap between global sea level estimates based on δ 18 O F and GIA analyses of geologic sea-level records. We find that the accuracy and precision of MIS 3 ocean temperature reconstructions is likely a key contributor, and various MIS 3 temperature reconstructions can reduce the “gap” by 30%–70% (∼10–20 m). Future improvements in the precision of temperature reconstructions will better constrain the ice volume component of δ 18 O F records. Ultimately, assessing the fidelity of δ 18 O F as a proxy for global ice volume is key to disentangling the feedbacks between climate and ice sheets over the Pleistocene.

Paleoceanography and Paleoclimatology↗

USGS2026

Terrestrial ecosystem response to changing temperature and seasonality in the Paleocene-Eocene Thermal Maximum: Shallow marine records from the Salisbury Embayment, USA

The Paleocene-Eocene thermal maximum (PETM, ∼56 Ma) is marked by a massive and rapid rise in atmospheric CO 2 and ∼5°C of global warming. It is globally characterized by a negative carbon isotope excursion (CIE), and, at least locally, is preceded by a pre-onset excursion (POE). We present palynological and bioclimatic analyses from stratigraphically expanded marginal marine sediment sections from the eastern United States. Late Paleocene forests were dominated by needle-leaved gymnosperms and broad-leaved angiosperms characteristic of warm climates. The POE is marked by a minor expansion of angiosperms and pteridophytes, warmer winters, and altered seasonal precipitation, followed by a return to pre-POE conditions. Increased terrestrial palynomorph concentrations before the CIE are suggestive of increased fluvial discharge before the PETM. Early PETM assemblages are characterized by dominance of ferns, loss of conifers, and expansion of broad-leaved angiosperm forests. Bioclimatic analyses indicate warmer mean atmospheric temperatures in early PETM time, driven primarily by winter warming of ∼3°C. A shift in seasonality, associated with increased severity of storms and floods that scoured the late Paleocene floodplain, facilitated establishment of riparian fern communities at the CIE onset. These flooding events persisted through the early part of the PETM and were severe enough to transport Westphalian-age (Middle Pennsylvanian) reworked material from the central Appalachian Basin and flush large amounts of terrestrial material and carbon onto the continental shelf, resulting in decreased salinity, increased productivity, and water-column stratification.

Delaware, Maryland, New Jersey, Virginia↗

USGS2024

20th century warming in the lower Florida Keys was dominated by increasing winter temperatures

Long-lived Atlantic coral species like Orbicella faveolata are important archives of oceanographic change in shallow, marine environments like the Florida Keys. Not only can coral-based records extend for multiple centuries beyond the limits of the instrumental record, but they can also provide a more accurate representation of in situ conditions than gridded interpolated sea-surface temperature (SST) products for nearshore reef environments. We use the coral Sr/Ca paleothermometer to produce a 150-year (1830–1980 C.E.) monthly SST reconstruction from an O . faveolata colony collected in the Marquesas Keys, FL, USA. An important feature of our record is a significant 20th-century warming trend in winter SSTs. We hypothesize that the winter warming trend was driven partially by a decrease in upwelling associated cyclonic eddies spinning off the Florida Current. A long-term weakening of winter Florida Current transport over the 20th century could be responsible for decreased cyclonic eddy formation in the Florida Straits. Another feature of the record is pronounced multidecadal fluctuations of mean annual warming and cooling in the record, which correspond to Atlantic Multidecadal Variability (AMV), with the AMV lagging behind western Florida Keys temperatures by 5–11 years. Strong coherence between coral-based SST reconstructions in the western Florida Keys with broader scale Atlantic oceanographic trends over the past century suggests a common driver of regional SST variability.

Florida↗