Biography：
Dr. Steiner is a marine biogeochemist who studies how interactions between the ocean and its boundaries facilitate the chemical composition of the ocean, and uses variability in seawater chemistry to quantify the function of the ocean as a carbon pump. Dr. Steiner obtained his PhD in Oceanography from the Hebrew University of Jerusalem in 2017 under the co-supervision of professors Jonathan Erez and Boaz Lazar. Following his doctorate studies, he conducted postdoctoral research at the University of Cambridge where he collaborated with professor Alexandra (Sasha) Turchyn on development of novel methods to quantify the marine inorganic carbon cycle. In 2019-2025 Dr. Steiner was a senior scientist at GEOMAR Helmholtz Centre for Ocean Research Kiel where he co-led several large research cruises aimed at investigating the distribution of trace metals in the ocean and their effect on the biological carbon pump. Dr Steiner recently joined the Institute of Earth Sciences at the Hebrew University of Jerusalem as a Senior Lecturer (equivalent to Assistant Professor).
Abstract：
The cations calcium, strontium and lithium are found in high dissolved concentrations in seawater and have much longer residence times in the ocean than the rate at which the ocean mixes. Despite the long residence times, we measure consistent variability of ~3% in the seawater concentrations of strontium and lithium, and 1.5% in calcium concentrations. This variability translates to very high turn-over rates which are the result of precipitation and dissolution of biogenic skeletons in the case of calcium and strontium, and inorganic silicate reactions in the case of lithium. We took advantage of the tendencies of different groups of organisms to precipitate skeletons with specific and unique chemical compositions, and found that nearly the entire variability in strontium concentrations can be attributed to strontium sulfate shells precipitated by unicellular Rhizaria of the class Acantharia. The flux of Acantharean shells required to produce the water column variability in strontium concentrations is <2% of the current calcium carbonate flux in the ocean, implying that minute changes in marine microplankton communities can make a big difference in the marine distribution of Sr/Ca ratios. The variability in lithium concentrations in the ocean is larger than we expected prior to this work, and implies higher rates of dissolution of aluminosilicate minerals and precipitation of new clay minerals than previously appreciated. The implication is that the inorganic silicate cycle may be an important buffer against abrupt changes in the chemistry of the ocean.
