Particle Flux in the Western Black Sea in the Present and over the Last 5,000 Years: Temporal Variability, Sources, Transport Mechanisms

The particle flux in the present and over the last 5,000 years was investigated in the Black Sea in a comparative study with samples from time-series sediment traps and laminated core sediments. The sediment trap samples were collected in the southwestern Black Sea over 2 1/2 years at sampling intervals of about two weeks. Sediment core samples were derived from the central part of the western Black Sea, deposited throughout the last 5,000 years during which the Black Sea was anoxic. Conclusions from this study shed important light on temporal and regional variability of the particle flux in the Black Sea, dominant particle sources, and particle transport mechanisms. Dominant particle sources are biogenic matter (coccolithophorids of the species Emiliania huxleyi, diatoms, and silicoflagellates) and terrigenous matter from the Danube and nearby local rivers. The relative importance in the supply of these particles varies annually and can be grouped into three phases: Phase I (June-October) coccolithophorid production, Phase II (November-January) resuspension of coccoliths and terrigenous matter, and Phase III (February-May) river input of terrigenous matter and production of diatoms and silicoflagellates. Once removed from the surface water, particles settle rapidly at a rate of 115 ±70 m/day. Regionally, the particle flux varies considerably. Throughout the last 1,000 years (sediment unit I), the particle flux (paleoflux) was more than 5 times larger in the central part of the western Black Sea than at present in the southwestern Black Sea, mostly because of the 11 times larger supply of coccoliths. The coccoliths were probably largely produced on or adjacent to the Danube shelf in the northwestern Black Sea and subsequently resuspended and transported offshelf by the fall storms. Terrigenous matter in the central part of the western Black Sea is higher by a factor of 3 compared to the southwestern Black Sea. The coccoliths are concentrated in the white laminae (>93 % CaC0 3 ), and if the seasonal dynamics in the particle supply at the sediment trap site is taken as a standard, the white laminae would be deposited between about June and January. The black laminae contain largely terrigenous matter and form during the peak river discharge period between about February and May. Compared to the last 1,000 years (unit I), the particle flux in the central part of the western Black Sea between 1,000 and 5,000 years B.P. was smaller by a factor of three, because the salinity was still too low during this time period for the coccolithophorid Emiliania huxleyi to exist. The Black Sea was a fresh water environment before more than 5,000 years ago and gradually became brackish; Emiliania huxleyi became established after the salinity exceeded 11 %.. The terrigenous matter supply remained about constant over the last 5,000 years. The western Black Sea is dominated by terrigenous input from the Danube as revealed by the illite/montmorillonite ratio. Seasonally, the terrigenous matter from the Danube appears to be traceable in the southwestern Black Sea, as seen by the Ti/Al and illite/montmorillonite ratios in the sediment trap samples. ACKNOWLEDGMENTS First and foremost, I am deeply indebted to Sus Honjo for his continuous and enthusiastic support and encouragement and for providing the motivating atmosphere to pursue new ideas. His patient confidence, which allowed me to participate in the Black Sea project, was greatly appreciated, as was his financial and logistical support. I am very grateful to my thesis committee for its constructive advice at every stage of the program. Discussions with Kozo Takahashi gave at lot of insight into the particle dynamics of the ocean. Bill Curry was very instrumental in keeping me in touch with reality in sedimentological questions and viewpoints. As a Black Sea expert, Dave Ross provided useful criticism at various stages to smoothly integrate the present work into the existing data pool without losing originality. Ed Boyle devoted a lot of effort to attach a critical geochemical angle to my geological background. John Southard was very helpful with his guidance during the first part of the JP at MIT. In addition, Jake Peirson and Mary Athanis were very supportive with their guidance along the administrative avenues with its occasional potholes (i.e. registration deadlines) of the MIT/WHOI joint program. I further thank Lloyd Keigwin for chairing my thesis defense. I was fortunate to work in a lab with responsible and vivacious people. The most important person to get me in touch with the hands-on aspects of particle collection on the ship and analysis in the lab was Steve Manganini, who also is just a great person to go on a cruise with. Emily Evans helped many times with logistical aspects during my studies. Amy Karowe was very helpful in the process of data collection and efficient data management, besides being a very supportive and pleasant housemate. Will Howard and Cindy Pilscaln expanded my understanding of marine sedimentation processes during numerous fruitful discussions. Vernon Asper spent considerable effort in showing me some of the ropes in the quantitative particle flux analysis. Ken Doherty and Rich Krishfield helped several times with technical aspects of the sediment trap moorings. Bonnie Woodward, Xia Qing, Susie Carter, and Abby Spencer were quick and very reliable in the chemical analysis of samples. I am likewise very grateful to the collaborating oceanographic team from the University of Hamburg, namely Drs. Egon Degens, Venu Ittekkot, and Stephan Kempe, who allowed me to subsample cores from their cruise to the Black Sea with the R/V CHAIN in 1975, which became an integral part of this thesis. Numerous discussions with each of my German colleagues were very valuable for the better understanding of the subject matter. Venu, who also served on my advisor committee, additionally made arrangements for my participation on the successful first Arabian Sea cruise in 1986, which further broadened my practical knowledge in international oceanography. My gratitude extends also to my Turkish colleagues, Drs. Erol Izdar and Tosun Konuk, as well as their students, who were very supportive and extremely helpful in all logistical aspects of the data collection during the cruises in the Black Sea, besides being very pleasant colleagues to collaborate with. I also thank the officers and crews of the R/V Koca Piri Reis for their high level of support during the cruises to the Black Sea, as well as the Hydrographic Institution, Ankara, for providing their long-term weather and river records on northern Turkey for this study. Further, I am very indebted to other colleagues who were instrumental in my studies. JoAnn Nicholson from Cornell University was a terrific collaborator in this Black Sea project on ship and in the lab with her high expertise in microbiology and biogeochemistry and her critical and thorough editing skills. Larry Poppe from the USGS supported me in the clay mineral analysis with his instrumentation. Don Bankston was invaluable with his expertise in elemental chemistry. John Jasper enlightened me many times in organic chemistry. Peter Schweitzer was a big help on numerous occasions in questions of quantitative data analysis. Glenn Jones and Alan Fleer allowed me to use their equipment several times. Kelly Luetkemeyer helped with the satellite image analysis on the remote sensing image processor. Steve Recca from MIT guided my research on the electron microprobe. LuPing Zou and Judy Commeau from the USGS helped a few times with the SEM analysis. My understanding of the Black Sea has been greatly improved by discussions with Hugh Livingston, Ken Buesseler, Peter Brewer, John 'Milliman, Frank Manheim, Ed Scholkovitz, Ian McCave, John Edmond, and others. Further, I would like to thank all my fellow students for providing a pleasant academic and social atmosphere for the prosperity of intellectual thoughts. This research was funded by National Science Foundation Grant No. OCE-8417106 and Office of Naval Research Contract No. N00014-85-C-0001.