Bernward J. Hay

Sediment deposition in the Late Holocene abyssal Black Sea with climatic and chronological implications

The temporal sedimentary patterns in the Late Holocene central eastern and western Black Sea are very similar. The sedimentary history was most visibly affected by the coccolithophorid species Emiliania huxleyi which briefly invaded the Black Sea for the first time (“First Invasion Period”), nearly disappeared again shortly afterwards (“Transition Sapropel”), but returned permanently several centuries later (“Final Invasion Period”). The temporary near-disappearance of E. huxleyi was probably caused by a temporary drop in salinity. Accumulation of E. huxleyi was on average about 40% higher in the western than in the eastern Black Sea. Highest coccolithophorid production occurred basin-wide during part of the Little Ice Age. The accumulation of terrigenous matter was generally higher in the eastern than in the western Black Sea by about 20%.

Varve calibrated records of carbonate and organic carbon accumulation over the last 2000 years in the Black Sea

Sedimentologic and geochemical studies of box and gravity cores recovered from the Black Sea during the first leg of a multileg international Black Sea expedition in 1988 allow reconstruction of the basinwide Holocene environmental history of the Black Sea. In the deeper parts of the basin, box cores typically recovered a flocculent surface layer (“fluff”), laminated coccolith marls of Unit I (25–45 cm thick), and the upper 5–10 cm of finely laminated, dark-colored sapropels of Unit II. Fine-grained, homogeneous mud turbidites are interbedded with Units I and II over much of the basin, but the stratigraphie position of these turbidites differs, from site to site. The deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae. Sediment trap deployments in the Black Sea suggest that light and dark laminae couplets represent annual increments of sedimentation (i.e., varves); we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events. Distinctive groups of laminae in Unit I can be correlated across the entire deeper basin (a distance of more than 1000 km). This implies a remarkable homogeneity in production, accumulation, and preservation of biogenic material over much of the Black Sea during deposition of Unit I. The change from deposition of finely laminated, organic carbon-rich sapropels (Unit II) to laminated, more calcareous, coccolith-rich marls (Unit I) is thought to represent the crossing of a salinity threshold for Emiliania huxleyi. The varve chronology sets this change at about 1.63 ka (1633±100 yr B.P.), but the record of magnetic secular variation measured in several cores produces an age estimate of about 2.0 ka for the base of Unit I, or about 1.2 times the varve age. The average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of Unit I is 2.7 ka, or about 1.7 times the varve age. Following the initial change to coccolith-dominated sedimentation, deposition of sapropel resumed for at least one significant period, 1.56–1.25 ka. Since 1.25 ka, cycles of carbonate deposition with quasi-decadal periodicities have produced characteristic darker and lighter assemblages of laminae. These cycles may have been climatically driven. Geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in Unit I (averaging 35–45 g m−2 yr−1) than in sapropelic Unit II. which contains primarily detrital carbonate. The accumulation of lithogenic components in parts of Unit I is only 1.5 times the rate in Unit II. Deepwater organic carbon accumulation rates are somewhat higher in Unit I (3.5–4.5 g m−2 yr−1) than in the upper part of Unit II. Organic carbon accumulation rates in Unit I are somewhat antithetic to those of carbonate, and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material, it appears that terrestrial organic matter is an important component (perhaps >25%) of total organic carbon burial in the basin. Unit I in the western part of the Black Sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than Unit I in the eastern part. This difference between eastern and western Black Sea is to be expected because of the major rivers that empty into the western Black Sea from eastern Europe, Ukraine, and Russia. Shallow slope sites, but still within euxinic bottom waters, have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites, suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center. A comparison of the Black Sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions. For a given bulk accumulation rate the organic carbon accumulation rates, normalized to primary productivity, are about the same in both settings.

Interannual variability in particle flux in the southwestern Black Sea

Abstract Vertical particle flux was measured at two sites in the southwestern Black Sea using automated time-series sediment traps over a period of 4.5 years. The particle flux between both sites varied considerably. (1) At site BSC (80 km from shore) the dominant fraction of the annual flux was deposited during short blooms; at site BS (40 km from shore, but still beyond the shelf break), the particle flux was less dominated by short-term blooms. (2) At site BSC, plankton blooms were the dominant cause for removal of suspended lithogenic matter; at site BS, vertical transport of lithogenic matter was linked also to the occurrence of storms and to high discharge periods of local rivers. Upwelling in the southwestern Black Sea may play an important role in triggering plankton blooms.

Scavenging and particle deposition in the southwestern black sea-evidence from Chernobyl radiotracers

The pulse of fallout tracers from the Chernobyl accident in April 1986 is used to examine scavenging and particle deposition in the southwestern Black Sea. Data on the distribution of Cs137, Cs134, Ru106 and Ce144 between the dissolved, suspended and sinking phases are presented. As expected by their different chemistries, the more particle-reactive Ru106 and Ce144 tracers are preferentially removed from surface waters relative to Chernobyl Cs, a predominantly conservative tracer. By comparing the tracer isotopic ratios in suspended fine particulates and rapidly sinking large particulates caught in sediment traps, an indication of the sediment source can be obtained. During the spring and summer, biological blooms drive rapid vertical transport of particles and tracer to depth, while during the autumn and winter months the lateral transport of shelf-derived particulates dominates the sinking flux. By the end of this annual cycle, much of the Chernobyl Ru106 and Ce144 have been scavenged from surface waters and removed to depth on sinking particles; however, there is significant release of these tracers back into the mid-waters during this process.

An assessment of the Nimbus-7/CZCS calibration for May 1986 using satellite and In situ data from the Arabian sea

Abstract During the intermonsoon period in May, pigment concentrations in the Arabian Sea are uniformly low, winds are light, and the atmosphere is relatively clear. During May 1986, a hydrographic survey of the central Arabian Sea was conducted, and stations were coordinated with Nimbus-7 / Coastal Zone Color Scanner (CZCS) overpasses. Because the calibration of the CZCS degraded severely during its lifetime (October 1978 to June 1986), pigment concentrations from 35 samples at four sites in the Arabian Sea are used to refine the calibration of the CZCS using a “vicarious” calibration technique. This calibration provides a final estimate of the sensors sensitivity loss for sensor Gain 2. The results show that the sensitivity losses during May 1986 were roughly 35%, 16%, and 9% at 433 nm, 520 nm, and 550 nm, respectively. Additional comparisons were made with the calibration used in the NASA CZCS global processing for May 1986. Assuming the same calibration correction at 670 nm as was used in the global processing, the global processing calibrations for 520 nm and 550 nm were found to be correct, but the calibration correction at 443 nm was found to overestimate the total radiance. Profiles of pigment concentration, temperature, salinity, and light attenuation are also used to describe the bio-optical characteristics of the Arabian Sea during the intermonsoon period as they pertain to the calibration.

Temporal and spatial variability in sedimentation in the Black Sea : cruise report R/V Knorr 134-8, Black Sea Leg 1, April 16-May 7, 1988

Funding was provided by the National Science Foundation nunder various grants to shipboard participants

Particle fluxes, south central Black Sea : 1982-1985

Annual particle fluxes were measured by sediment traps deployed at a station about 40 km north of Amasra, Southern Black Sea, by an international team of oceanographers from Germany, Turkey, and the United States. This experiment continuously monitored oceanic particle flux for two and a half years at approximately two-week intervals at 250 m and 1200 m below the surface using 1.2sq.m Mark 5-12 time-series sediment traps. The water depth at this station was about 2,000 m and both traps were situated within the anoxic layer of the Black Sea. The collected flux samples were analyzed at the Wood Hole Oceanographic Institution to document the basic sedimentary characteristics using a quarter of each sample split. In the first data file from this experiment, total mass, carbonate, noncombustible, combustible, opal (biogenic silica), organic carbon, and organic nitrogen fluxes data are presented in bar graphs and detailed tables, in unit samples covering a two-week period at each depth. The Black Sea Sedimentation Data File is intended to provide source data on particle fluxes from this unique ocean environment for further investigation and for planning advanced research programs.