Peta J Mudie

Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence

Multi-proxy data and radiocarbon dates from several key cores from the Black Sea and Marmara Sea document a complex paleoceanographic history for the last V30 000 yr. The Marmara Sea was isolated from both the Black Sea and the Aegean Sea during glacial periods when global sea-level lowering subaerially exposed the shallow sills at the Straits of Bosphorus and Dardanelles (i.e. lake stage), and reconnected through both straits during interglacial periods, when rise of global sea level breached the shallow sills (i.e. gateway stage). Micropaleontological data show that during the ‘lake stage’ the surface-water masses in both the Marmara Sea and Black Sea became notably brackish; however, during the ‘gateway stages’ there was a low-salinity surface layer and normal marine water mass beneath. Two sapropel layers are identified in the Marmara Sea cores: sapropels M2 and M1 were deposited between V29.5 and 23.5 ka, and V10.5 and 6.0 ka, respectively. Micropaleontological and stable isotopic data show that the surface-water salinities were reduced considerably during the deposition of both sapropel layers M2 and M1, and calculation using planktonic foraminiferal transfer functions shows that sea-surface temperatures were notably lower during these intervals. The presence of fauna and flora with Black Sea affinities and the absence of Mediterranean fauna and flora in sapropels M1 and M2 strongly suggest that communication existed with the Black Sea during these times. A benthic foraminiferal oxygen index shows that the onset of suboxic conditions in the Marmara Sea rapidly followed the establishment of fully marine conditions at V11^10.5 ka, and are attributed to Black Sea outflow into the Marmara Sea since 10.5 ka. These suboxic conditions have persisted to the present. The data discussed in this paper are completely at odds with the ‘Flood Hypothesis’ of Ryan et al. (1997), and Ryan and Pitman (1999). Crown Copyright > 2002 Elsevier Science B.V. All rights reserved.

Dinoflagellate cysts, freshwater algae and fungal spores as salinity indicators in Late Quaternary cores from Marmara and Black seas

Abstract Seismic profiles and mollusks have been used to suggest that from ∼12u2008500 to 7000 yr BP, the Black Sea was an isolated freshwater lake containing potable water and implying a surface salinity of 24, and that Spiniferites cruciformis, Spiniferites inaequalis, Peridinium ponticum, Polykrikos spp. and Quinquecuspis concreta characterize the lower salinity of the Marmara and/or Black seas. The core-top data and correlatable down-core assemblage changes in time-equivalent sapropelic and brown muds show that there is no evidence for differential aerobic decay of dinocysts in the study area. The main acritarchs are Sigmopollis psilatum, Concentricystes cf. C. rubinus and cf. Acritarch-8 of Traverse (1978), all of which are absent from the Aegean Sea and decrease in abundance with increasing salinity; the first two taxa have been reported previously as freshwater species. Fungal remains show a similar distribution pattern to the freshwater acritarchs, indicating their origin from terrestrial environments. Freshwater Chlorococcales are almost confined to the Black Sea but they have rare occurrences in the Aegean, indicating long-distance transport. Microforaminiferal linings are abundant in the Marmara Sea but are absent in deep water of the Black Sea. In the Marmara Sea, mid–late Holocene assemblages (

Pollen stratigraphy of Late Quaternary cores from Marmara Sea: land^sea correlation and paleoclimatic history

Marine pollen analysis is an important tool for paleoclimatic reconstruction of regions like the eastern Mediterranean and Near East where few onshore sites provide long pollen records. First, a compilation was made of core-top data from the eastern Mediterranean to BlackSeas to map regional variations in modern marine pollenspore concentrations. These data show a strong linkbetween pollen-spore concentrations and sea surface salinity, with minima of 5 grains/g in the southern Mediterranean and maxima of 160 000 grains/g in the BlackSea. Despite under-representation of some forest and herbaceous vegetation indicators, e.g. Fagus and Pistacia, variations in species composition of the marine assemblages correspond closely with the distribution of regional vegetation zones and can be used as proxies for spatial differences in seasonal and total temperature and rainfall. Pollen-spore assemblages in five cores from the Marmara Sea with multiple ages ranging from 33 550 to 1990 yr BP and one Holocene core from southeastern BlackSea were used to compile a Late Quaternary marine pollen stratigraphy. These data were then compared with eastern Mediterranean onshore reference sites in order to reconstruct a vegetation and paleoclimate history for the BlackSea^Aegean corridor from the Pleniglacial interval to present. Five marine pollen zones are recognized. PZ-5 (V33.6^24 ka) corresponds to the late Wu « rm Pleniglacial; PZ-4 (V24^ 13 ka) spans the Late Glacial Maximum (LGM); PZ-3 (V13^10.2 ka) includes the Allero « d^Younger Dryas glacial^ interglacial transition; PZ-2 (10.2^4 ka) marks the early Holocene interglacial warm, wet interval; and PZ-1 covers the latest Holocene colonization phase, which may also have been cooler and drier. Using the steppe^forest index of Traverse (1975), it is shown that the only intervals of severely dry conditions occurred briefly during the LGM and its transition; during most of the Pleniglacial and all of the Postglacial time, precipitation versus evaporation rates were sufficiently high to permit persistence of oro-Mediterranean forest vegetation. Furthermore, there is no evidence for environmental conditions in the BlackSea^Marmara region that would have encouraged pastoral or agricultural settlement in the littoral region prior to the Bronze Age, commencing 4600 years ago. Crown Copyright A 2002 Elsevier Science B.V. All rights reserved.

Paleoclimatic and paleoceanographic conditions leading to development of sapropel layer S1 in the Aegean Sea

Abstract Sapropel S1 occurs as 25–35 cm-thick black, weakly laminated muds in Aegean Sea cores. S1 was deposited between 9600 and 6400 yr B.P., during a period of isotopically depleted and relatively cool surface waters. Micro-faunal and -floral data indicate a major reduction in surface waters salinity during the deposition of S1, and oxygen isotopic data show a northerly fresh water source. Relatively light δ 13 C org and high pollen-spore concentrations in S1 suggest increased influx of terrestrial organic carbon, probably supplied by major rivers draining into the northern Aegean Sea. Benthic foraminifera indicate high-nutrient, low oxygen bottom waters for S1, and together with silt-sized hematite and manganese coatings suggest that during the deposition of S1 surface sediments were oxic. Visual and XRD evidence of pyrite in S1, together with enrichments in S, Cu, Zn, As, Ni, Cr and Fe suggest that subsurface conditions were sufficiently reducing for SO 4 2− reduction to occur, probably by diffusion from surface oxic into subsurface anoxic sediments. Palynomorphs in S1 show large increases in terrestrial pollen and spores, with the floral assemblage indicating significant influx from northern European rivers, and minor African components associated with increased summer monsoonal rain. Abundance of dinoflagellates and amorphogen suggests some increase in primary productivity in response to increased influx of humic compounds, however, there is no evidence of upwelling. The clay fraction in S1 shows notable decreases in smectite and kaolinite and reciprocal increases in illite and chlorite. The combined data suggested that the evolution of S1 in the Aegean Sea largely resulted from stagnation of the surface waters during the final disintegration of the continental ice sheets, rather than an increase in primary productivity and higher preservation of organic carbon on the sea floor.

Late glacial-Holocene paleoclimatic and paleoceanographic evolution of the Aegean Sea: micropaleontological and stable isotopic evidence

Abstract Late glacial to Holocene paleoclimatic and paleoceanographic changes are examined using records of calcareous and organic-walled marine microfossils, pollen and terrestrial spores and oxygen isotope data in cores from the Aegean Sea basins. Planktic foraminiferal, coccolith and dinoflagellate data show that the late glacial-Holocene transition in the region was associated with a large warming of surface water. Mediterranean-based paleotransfer functions for planktic foraminifera show a 5 °–10 °C increase in surface water temperature from ~14,000 to ~9600 yr B.P. Estimates of surface water oxygen isotopic composition ( δ 18 O w ) derived from planktic foraminiferal oxygen isotopic and transfer function data indicate that this warming was associated with a 2.0 to 2.5‰ reduction in δ 18 O w . Transfer function results indicate corresponding 1.0 to 1.5‰ salinity reductions for this tim (ca. 6400–9600 yr B.P.) throughout the Aegean Sea. Pollen, dinoflagellate and isotopic data show that the early Holocene excess fresh water originated from rapid melting of the northern European and Siberian ice sheets, supplied primarily from the Black Sea by the opening of Bosphorus and Dardanelles Channels, during the post glacial sea-level rise, and supplemented by major rivers entering the Aegean Sea. Continuous outflow of fresh water into the Aegean Sea provided a low salinity surface lid, preventing the ventilation of the deep water. Benthic foraminifera shows a major turn-over that indicates low dissolved oxygen; however, bottom waters were not anoxic. Sapropel level S1 resulted from a combination of stagnant deep water in isolated depressions, increased terrigenous organic matter and periods of high primary productivity, as indicated by pollen and dinocysts, respectively. The surface water temperature and salinity reached present-day values at ~6400 yr B.P., with little subsequent change despite the major deforestation onshore.

Late glacial, Holocene and modern dinoflagellate cyst assemblages in the Aegean–Marmara–Black Sea corridor: statistical analysis and re-interpretation of the early Holocene Noah’s Flood hypothesis

Understanding of the history of water exchange between the Mediterranean and Black seas has been hampered by the lack of continuous microfossil records for Holocene cores from the Marmara Sea Gateway (Aegean–Marmara–Black Sea corridor), and by the lack of core-top data linking modern microfossil assemblages with sea surface conditions. Based on molluscs, an abrupt transition from freshwater to marine conditions at ca. 7.5 ka has been postulated, with interpretation of this event as the basis for the story of Noah’s Flood. We have re-examined this hypothesis using organic-walled dinoflagellate cysts that show excellent preservation and moderate to high diversity in Pleistocene–Holocene sediments of the Marmara Sea Gateway. Principle component analysis of 16 core-top samples shows that an assemblage dominated by cysts of autotrophic gonyaulacoids distinguishes the hypersaline Aegean–Mediterranean water (salinity 31–38), whereas heterotrophic protoperidinioids characterise the low-salinity Marmara–Black Sea water (salinity ∼14–25). About 150 samples from eight cores, with multiple radiocarbon ages spanning the past ∼33 000 years, show correlatable major changes in cyst assemblages along the Marmara–Black Sea corridor. Variation in length and shape of gonyaulacoid species processes decreases upcore from basal units where there are no-analogue assemblages of cysts with highly variable spine development. It is shown that these variable and no-analogue assemblages correspond to brackish conditions (salinity ∼4–12) when calibrated against δ18O data and salinity estimates derived from planktonic foraminifera. Salinity reconstructions indicate that the Aegean and Marmara seas were connected by ∼11 ka when the Marmara Sea was a brackish or low-salinity sea (∼12–17) and that the Black Sea was flowing into the Marmara Sea by at least 10.2–9.5 ka. There is no evidence to support either the idea that the Black Sea was a large freshwater lake suitable for farming in the early Holocene or that a sudden (<500-yr) flooding of the Black Sea by a 100-m-high waterfall of Mediterranean water occurred at 7.5 ka. It is shown that there is a need for precise use of salinity terms when reconstructing the history of saline lakes in the context of Neolithic human occupation so that the likelihood of agricultural settlement can be evaluated realistically.

Origin of late glacial—Holocene hemipelagic sediments in the Aegean Sea: clay mineralogy and carbonate cementation

Abstract Four hemipelagic lithological units are identified in the late glacial to Holocene sediments in the Aegean Sea. These lithologies are silty-clay and clay in texture and include a varying mixture of loose terrigenous sediments supplied from the adjacent landmass, gravel- to sand-sized cemented carbonate clasts and nodules, sand- to silt-sized air-born volcanic debris and biogenic remains. Sediment dispersal during the past 14,000 years was controlled mainly by the fluvial discharge rate, by sea-level variations which determined the proximity of basins to river mouths and by oceanographic conditions in the Aegean Sea. Cemented carbonate clasts and nodules occur in all sediments except Unit C (sapropel S1). They are well- to friably-cemented, mottled to peloidal micrite or microcrystalline inter-granular cement between terrigenous and bioclastic debris, and the carbonate is 10–11 mole % magnesium calcite. During the deposition of sapropel S1 (Unit C) the Aegean Sea was strongly stratified, with colder, more saline water masses occupying the deep basins, which prevented the development of cemented carbonate nodules and clasts. Aragonite, as pteropods and microcrystalline aragonite is present throughout the cores, and together with the cemented carbonate clasts and nodules, show that shallow pore waters in the Aegean Sea have been saturated to supersaturated with respect to both aragonite and magnesium calcite for at least the past 14,000 years. Results of XRD studies show that Unit C (sapropel S1) is characterized by lower smectite and kaolinite and higher illite and chlorite than the other units. Lower smectite/illite and kaolinite/chlorite ratios in Unit C may reflect increased supply of illite and chlorite from European lowland rivers flowing into the Black Sea, from rivers discharging directly into the northern and eastern Aegean Sea, and decreased supply of kaolinite which is mainly of North African origin.

ORGANIC GEOCHEMICAL AND PALYNOLOGICAL EVIDENCE FOR TERRIGENOUS ORIGIN OF THE ORGANIC MATTER IN AEGEAN SEA SAPROPEL S1

AbstractOrganic geochemistry and micropaleontology are used to determine the origin of sapropel S1 in the Aegean Sea.Low-molecular-weight (C 15 ,C 17 and C 19 ) n-alkane data show that net primary productivity (NPP) increased from˘14,000to 10,000 yr BP at the glacial interglacial transition, but the onset of S1 at 9600 yr BP marks a sharp decline in NPP, whichremained low until ˘8200 yr BP. The start of sapropel deposition is marked by increased total organic carbon (TOC)and pollen-spore concentrations, together with increased high-molecular-weight (C 27 ,C 29 ,C 31 and C 33 ) n-alkanes. Pollenassemblages show large influx of tree pollen from central-northern European forests. Increases in high-molecular-weightn-alkanes suggest greater influx of fresh vascular plant material at the start of S1, although the amount is small comparedto other insoluble organic matter. Palynological studies showed that most of this insoluble organic matter are flocksof dark-brown amorphous kerogen, typical of terrigenous humic compounds. From ˘8200 yr BP to the top of S1at ˘6400 yr BP, there is a decline in high-molecular-weightn-alkanes and terrigenous kerogen, and an increase inlow-molecular-weightn-alkanes, suggesting that NPP recovered during the later deposition of S1 in the Aegean Sea. Theincrease in low-molecular-weightn-alkanes coincides with the recovery of coccolithophores and dinoflagellates, suggestingthat these phytoplankton are primarily responsible for the low-molecular-weightn-alkane variations. These data from theAegean Sea support the model for sapropel deposition resulting from increased influx of TOC during times of stagnantbottom water, but disagree with Mediterranean models prescribing a large increase in marine productivity. uf6d91999 ElsevierScience B.V. All rights reserved.Keywords: sapropel S1; Aegean Sea; fatty acids; n-alkanes; palynology

Ocean-atmosphere responses to climatic change in the Labrador Sea: Pleistocene plankton and pollen records

Abstract Pleistocene climate change is examined using proxy-climatic records from oxygen isotope data, calcareous and organic-walled marine microfossils, pollen and terrestrial spores deposited during the past 0.9 Ma at ODP Site 646 in the Labrador Sea, 500 km north of the present polar front. Paleotransfer functions applied to planktonic foraminiferal assemblages show relative increases in interglacial summer (3–7°) and winter (3–5°) temperatures and in winter salinity (0.5–2%‰) for the past 0.4 Ma, but only two earlier intervals (early stage 11 and stage 17) have changes of comparable magnitude. Coccolith and dinoflagellate cyst accumulation rates show that primary productivity is generally correlated with temperature and salinity changes at the start of interglacials. These productivity peaks lag the ice volume changes by 2–4 ka. Dinocyst blooms seem to precede coccolith peaks, reflecting the tolerance of opportunistic species for large variations in temperature and salinity. Peaks in pollen and spore abundance are strongly correlated with ice volume which controls the position and stability of the polar jet stream in addition to the northern extent of forest vegetation. Time series analysis was made of 7 oceanographic variables (SST summer and winter, surface salinity, coccoliths, dinocysts, planktonic and benthic foraminifera) and 5 other variables (δ18, pollen-spores, percent sand, foraminiferal test fragmentation and reworked palynomorphs). Most variables showed significant power peaks at ≈ 100 Ka, and/or at ≈ 41 ka. However, sea surface responses showed minor peaks at 26 and 16 ka, and microfossil productivity also showed significant peaks at 68 Ka. The high latitude Labrador Sea records thus display large non-linear regional responses to climate changes in addition to the effects of orbital insolation forcing at ≈ 41 and ≈ 23 ka.

Decadal-scale sea ice changes in the Canadian Arctic and their impacts on humans during the past 4,000 years

Abstract Climate warming of >1.5°C over three decades has diminished Arctic sea ice and forced drastic changes on Inuit people of the Canadian Arctic. Discontinuities in archaeological records also suggest that climatic changes may have caused site abandonment and life style shifts in Paleo- and Neo-eskimo societies. We therefore examine the decadal-scale palaeoclimatic changes recorded by quantitative palynological data in marine records from Coburg Polynya, near Palaeo- and Neo-eskimo settlements on the North Devon Lowlands, and from the North Water Polynya between Canada and Northwest Greenland. Palaeotransfer functions from dinoflagellate cyst assemblages provide quantitative estimates of changes in sea surface temperature (SST) and sea ice cover (SIC) with the accuracy of historical measurements. Both sites record temperature variations of 2–4°C corresponding to changes in hunting modes and occupation-abandonment cycles on Devon and Ellesmere Islands. Our data show that from ∼6500 to 2600 BP, there were large oscillations in summer SST from 2–4°C cooler than present to 6°C warmer and SIC ranged from 2 months more sea ice to 4 months more open water. The warmer interval corresponds to the period of pre-Dorset cultures that hunted muskox and caribou. Subsequent marine-based Dorset and Neo-eskimo cultures correspond to progressively cooler intervals with expanded sea ice cover. The warming took ∼50–100 years and lasted ∼300 years before replacement by colder intervals lasting ∼200–500 years. These climate oscillations are more rapid than the archaeological cultural changes, but are of similar length to successive Palaeoeskimo occupations in the Nares Strait region.