Water Masses, Circulation Patterns, and Variability in the Central Arctic Ocean: Tracer Studeis (Tritium/3He, Oxygen Isotopes, and 14C) During the 2005 Arctic Section

This work will support the collection, measurement and analysis of tracers (tritium/3He, oxygen isotopes, and 14C) during the planned 2005 trans-Arctic cruise of the Swedish icebreaker ODEN, likely as a two-ship operation with the US Icebreaker Healy. The cruise track will cross the entire central Arctic, starting from the Alaskan Shelf crossing the central Canadian Basin to the Pole, from where it leads across the Eurasian Basin to the continental shelf north of the Barents Sea. This section offers the first opportunity to obtain a high-quality, high-resolution, full-depth multi-tracer data set in the central Canada Basin. In the context of the hydrography/tracer program scheduled to be carried out from the ODEN the PIs will collect and measure 900 tritium and helium isotope, 720 oxygen isotope, and 120 radiocarbon (14C) samples. These numbers of samples are adjusted to the scientific goals addressed with the individual tracer measurements. Accommodation on the ODEN for personnel to collect the tracer samples is being provided generously by Swedish colleagues. The proposed work will significantly enhance tracer studies in the Arctic Ocean by providing the first high-quality tracer data set from the poorly sampled Canadian Basin. They also will allow a look at decadal variability in the Eurasian Basin. Finally, the data will provide an extension of the global CLIVAR/carbon repeat hydrography program to the high northern latitude and will represent a firm baseline against which future sections can be compared to study possible anthropogenically driven change in the Arctic. The tracer data will be used to address the following scientific questions: (a) Determine freshwater distribution and inventories over the main basins of the Arctic Ocean and freshwater sources (meteoric water (river runoff and precipitation), sea ice meltwater and Bering Strait Inflow). (b) Explore changes in the freshwater inventory over the Nansen and Amundsen basins compared to those observed along sections occupied in 1991 and 1996 (decadal variability). (c) Determine circulation patterns of the upper waters (surface, halocline, and Atlantic-derived waters). (d) Examine mid-depth circulation patterns in the central Arctic Ocean. (e) Determine the mean residence times and age gradients in the deep waters in the Canadian Basin. The tracer data will be collected and interpreted in close cooperation with the other oceanographic programs on ODEN. The program addresses objectives of ARCSS, SEARCH, and ASOF, as well as high-latitude CLIVAR. Broader Impacts: The program will help to determine to which degree the wide range of changes that have recently been documented in the Arctic are part of natural variability or change due to human activities. This question has important societal relevance because a change towards a new state of the arctic system would have global ramifications for climate, as well as economy. Many indicators hint at the latter scenario, but we still lack the scientific certainty for an anthropogenically driven change of the arctic system. Additional broader impacts include the availability of high-quality data sets from the Arctic that will be used to assemble global data sets for climate and carbon studies (tracer measurements are an important element for estimating the amount of anthropogenic carbon in the ocean). On the educational side, the data will be available to students working on high latitude problems, and the results will be posted on a web site. The material is also routinely used in advanced courses taught at Columbia University. The material is typically used in case studies in courses on tracer oceanography or environmental tracer techniques. The data are also used by students for term papers or problem sets. Finally the PIs are establishing a program with high schools that will allow students to closely follow the evolution of scientific knowledge by involving them in each part of the proposed work.