Previous studies show evident increase of freshwater content in the Arctic Ocean and other regions using conventional measurements such as the expendable bathythermographs (XBT), bottle, mechanical bathythermographs (MBT), and Conductivity-Temperature-Depth (CTD) casts. A new strategy (Lagrangian type) was developed to sample the world ocean since the Argo floats first came into practice in early 1990s. Currently, there are 3308 Argo floats all over the world ocean.

Global Temperature and Salinity Profile Program (GTSPP) is a cooperative international project since 1990. The GTSPP handles all temperature and salinity profile data including XBT, CTDs, thermistor chain data, and Argo observations. These data will reach data processing centers of the Program through the real-time channels of the IGOSS program or in delayed mode through the IODE system. Real-time data in GTSPP are acquired from the Global Telecommunications System in the bathythermal (BATHY) and temperature, salinity & current (TESAC) codes forms supported by the WMO. Delayed mode data are contributed directly by member states of IOC. Near-real time gridded (T, S) dataset was established from GTSPP since 1990 with horizontal resolution of (1oŚ1o) and temporal increment of 1 month using the recently developed optimal spectral decomposition (OSD) method. With this new monthly varying gridded dataset, the upper ocean freshwater content (surface to 300 m depth) FWC300 was calculated at each horizontal grid point.

The empirical orthogonal function (EOF) analysis was conducted on the temporally varying global 2D FWC300 anomaly relative to its seasonal variation. The EOF-1 mode (73.7% variance) represents near global-scale variability with the largest anomaly appearing in the Indian Ocean near southeast of Africa. The first principal component (PC1) shows decadal variability. The temporal-spatial variability represented by the EOF-1 mode shows rapid increasing of global FWC300 from 1999 to 2005 and sustaining the high values after 2005. Interpretations of the observational results to recent global warming will also be presented.

References

Chu, P.C., L.M. Ivanov, T.P. Korzhova, T.M. Margolina, and O.M. Melnichenko, 2003: Analysis of sparse and noisy ocean current data using flow decomposition. Part 1: Theory. Journal of Atmospheric and Oceanic Technology, 20 (4), 478-491.

Chu, P.C., L.M. Ivanov, T.P. Korzhova, T.M. Margolina, and O.M. Melnichenko, 2003: Analysis of sparse and noisy ocean current data using flow decomposition. Part 2: Application to Eulerian and Lagrangian data. Journal of Atmospheric and Oceanic Technology, 20, 492-512.

Chu, P.C., 2011: Global upper ocean heat content and climate variability. Ocean Dynamics, in press.