Project Details
Projekt
Analysis of magnitude, drivers, and mechanisms of salinity variability in the tropical Atlantic
Applicant
Professor Dr. Peter Brandt
Subject Area
Oceanography
Term
from 2013 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 198122929
The ocean plays an essential role in the global water cycle. While during the first phase of the DFG Forschergruppe, the focus was on the equatorial Atlantic, during the second phase it is on the tropical North Atlantic, a region affect by intense precipitation. Sea surface salinity (SSS) in this region is highly variable on space scales ranging from small scales, associated with convective rain cells, to the basin scale, associated for example with the Intertropical Convergence Zone (ITCZ) spanning from South America to Africa. Temporal variability again is associated with sporadic rainfall events with time scales of few hours, daily cycles in near surface stratification and mixing, ocean mesoscale dynamics with time scales of weeks to few months, seasonal variability mainly associated with the seasonal migration of the ITCZ (Fig. 1) and interannual to decadal variability associated with the dominant climate modes of Tropical Atlantic Variability. The proposed project relies on satellite data and on data acquired in the tropical North Atlantic in the frame of different projects, including the SFB 754. Here we use the large amount of CTD profiles taken since 2006 mainly along the 23°W section between 15°N and 5°S (Fig. 2), together with shipboard and glider data taken in the wider region of the tropical North Atlantic. The large amount of salinity profiles allows to characterize the near-surface salinity variability and to combine this information with SSS from satellite remote sensing. The glider data that particularly include a large amount of microstructure profiles of the near-surface ocean are ideally suited to study near surface diapycnal freshwater fluxes. Main goal of the proposed project is to improve our understanding of the hydrological cycle in the salinity minimum region of the tropical North Atlantic with focus on oceanic freshwater fluxes and near surface freshwater budgets with implications for the understanding of long-term climatedriven changes. More specifically we will address the following topics: 1) interannual variability of SSS in the region below the ITCZ associated with large-scale climate modes, 2) the seasonal mixed layer freshwater budget with focus on diapycnal mixing and the role of near-inertial waves forced by highly variable winds close to the ITCZ, and 3) the near surface stratification variability associated with rainfall events and diurnal to multi-diurnal warm layers and its effect on SSS as observed by satellite remote sensing. The gained knowledge and available datasets will be used to assess the quality of model simulations with and without data assimilation and will contribute to increase the understanding of drivers and mechanisms of SSS variability. The proposed study is strongly related to the international program SPURS-2 that will focus on the salinity minimum region of the eastern tropical Pacific in 2016-2017.
DFG Programme
Research Units
Co-Investigator
Dr. Johannes Karstensen
Cooperation Partners
Dr. Marcus Dengler; Dr. Gerd Krahmann
