DOI: 10.25921/tf1k-ra58
title: NOAA/WDS Paleoclimatology - Black Sea Holocene Sediment Geochemical Data

description: Leg 1 of the 1988 R/V Knorr expeditions to the Black Sea recovered 90 gravity and box cores. The longest recovery by gravity cores was about 3 meters, with an average of about 2.5 meters, recovering all of the Holocene and upper Pleistocene sections in the Black Sea. During the latest Pleistocene glaciation, sea level dropped below the 35-meters-deep Bosporus outlet sill of the Black Sea. Therefore throughout most of its history the Black Sea was a lake, and most of its sediments are lacustrine. 

The oldest sediments recovered (older than 8,000 calendar years) consist of massive to coarsely banded lacustrine calcareous clay designated as lithologic Unit III, generally containing less than 1 percent organic carbon (OC). The base of overlying Unit II marks the first incursion of Mediterranean seawater into the Black Sea, and the onset of bottom-water anoxia about 7,900 calendar years. Unit II contains as much as 15 percent OC in cores from the deepest part of the Black Sea (2,200 meters). The calcium carbonate (CaCO3) remains of the coccolith Emiliania huxleyi form the distinctive white laminae of overlying Unit I. 

The composition of Unit III and Unit II sediments are quite different, reflecting different terrigenous clastic sources and increased contributions from hydrogenous and biogenic components in anoxic Unit II sapropel. In Unit II, positive covariance between OC and three trace elements commonly concentrated in OC-rich sediments where sulfate reduction has occurred (molybdenum, nickel, and vanadium) and a nutrient (phosphorus) suggest a large marine source for these elements although nickel and vanadium also have a large terrigenous clastic source. The marine sources may be biogenic or hydrogenous. A large biogenic source is also suggested for copper and cobalt. Because abundant pyrite forms in the water column and sediments of the Black Sea, we expected to find a large hydrogenous iron component, but a strong covariance of iron with aluminum suggests that the dominant source of iron is from terrigenous clastic material. Most elements in lacustrine Unit III sediments have a strong covariance with Al indicating a very dominant terrigenous source. In Unit II, some elements, especially nickel, molybdenum, vanadium, and zinc, do not correlate with aluminum and have concentrations well above terrigenous clastic material, indicating a marine source.
description: Leg 1 of the 1988 R/V Knorr expeditions to the Black Sea (Honjo et al. 1988) 
recovered 28 box cores that provide undisturbed, laminated sequences of late 
Holocene sediment from the southern half of the Black Sea.  A gravity core 
was attempted at most stations occupied during the cruise.  The gravity corer 
used a standard stainless-steel core cutter attached directly to a 5-m-long 
section of 4-in (10.2-cm) diameter, thick-walled PVC water-well casing. 
The core barrel was attached to a 167-kg weight stand, and the entire rig 
lowered at a winch speed of about 125 m/min at penetration.  Average recovery 
of 62 gravity cores was about 250 cm with maximum length of 500 cm. 
Cores were recovered in a vertical position, the overlying water was drained 
off, and the PVC core barrel was cut and capped before lowering to a horizontal 
position so that core tops were preserved.  Cores were cut into 1.0- to 1.5-m 
sections, capped, sealed, labeled, and stored vertically at 9°C in a 
refrigerated van.  Due to time limitations and lack of facilities, 
only two gravity cores were opened on board.  These cores were sectioned 
into 50-cm lengths and extruded with a fixed piston into presplit sections 
of 4-in (10.2-cm) PVC pipe.  After the presplit halves were separated, 
one half was used for pore-water squeezing and the other half was photographed, 
described, and saved as an archive.  Additional gravity-core sections were 
split longitudinally at Woods Hole into working and archive halves. 
The archive halves of two gravity cores were shipped to the University of 
Rhode Island for magnetic secular variation studies (Arthur and others, 1994). 
Working halves gravity cores were sampled at Woods Hole Oceanographic 
Institution for inorganic geochemical analyses at the USGS, Denver, Colorado, 
and carbon analyses at the University of Rhode Island. 

Age Model
Dating of Unit I was by 32 accelerometer mass spectrometry (AMS) radiocarbon 
dates and varve counts on sediments from subcores of box cores (Arthur et al. 
1994; Jones and Gagnon 1994; Arthur and Dean, 1998). The unit I/II and II/III 
boundaries in six gravity cores were dated by AMS (Jones and Gagnon, 1994). 
A Santorini volcanic ash layer, dated at 3350±75 calendar years, was identified 
in two gravity cores (Guichard and others, 1993).  Finally, geomagnetic secular 
variation events reflected in inclination and declination data from two cores 
provide datums that allow us to assign ages to points in Unit II (Arthur et al. 
1994; Arthur and Dean, 1998).  All calibrated ages are expressed in thousands 
of calendar years before present (cal. ka BP), where "present" is AD 1950, 
and ranges of ages are expressed in thousands of years (ky). 

Geochemical Methods
Carbon Analyses
Concentration of total carbon (TC) and total inorganic carbon (TIC) was determined 
by coulometric titration of CO2 following extraction from the sediment by combustion 
at 950°C and acid volatilization, respectively (Engleman et al., 1985).  
Weight percent TIC was converted to weight percent CaCO3 by dividing the fraction 
of carbon in CaCO3 by 0.12.  Total organic carbon (TOC) was determined as the 
difference between TC and TIC.

Inorganic Geochemical Analyses
For inorganic geochemical analysis, splits of powdered samples used for carbon 
analyses were analyzed for major, minor, and trace elements by induction-coupled, 
argon-plasma emission spectrometry (ICP, Briggs, 2002).