Studies of large-scale intermediate and deep water circulation and ventilation in the North Atlantic, south Indian and northeast Pacific Oceans, and in the East Sea (Sea of Japan), using chlorofluorocarbons as tracers.

摘要

Dissolved chlorofluorocarbons (CFCs), CFC-11 and CFC-12, were measured as time-dependent tracers in the subpolar North Atlantic, subtropical South Indian, subtropical Northeast Pacific Oceans, and in the East Sea (Sea of Japan). The CFC concentrations and derived apparent ages are used to determine the main pathways and ventilation rates of water masses. The decreasing trend of the atmospheric CFC-11/CFC-12 ratio after the late 1980s is used for the first time in estimating recent CFC ratio ages of upper ocean waters.; The most prominent CFC signal of the Labrador Sea Water (LSW) was observed in the Irminger Basin in 1997, and the rapid surge of LSW observed in 1994 was followed by a relative stagnation period. The LSW is the most dominant source of the Middle Irminger Water in the western Iceland Basin. The Antarctic Intermediate Water in the Indian Ocean was observed at 20°S in 1995 to spread northward mainly through 55–75°E and 90–100°E longitude bands with a relatively uniform CFC ratio age. The young Subantarctic Mode Water was prominent in the Southeastern Indian Ocean. The northward flowing CFC-bearing bottom water at 20°S in the Indian Ocean was detected in the deep Mascarene Basin with marginal CFC-11 signals. CFC ages were constant between 1982 and 1994 at the Northeast Pacific Ocean thermocline, although CFC concentrations have increased with time, indicating that the system is under a steady ventilation from the source area to this region. A smaller fraction of these waters is apparently ventilated during El Niño years due to the enhanced influence of tropical waters. The CFC penetration observed throughout the water column of the East Sea in 1996, and the high CFC inventory in these waters suggest active ventilation. The CFC maximum of the East Sea Intermediate Water was found over a wide area. Deep waters were more ventilated along the boundary regions than in the central part of the Japan Basin. Water exchange rates, residence times and mixing ages of water masses of the East Sea are estimated using a CFC-calibrated simple model.