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Project OC1
Seasonal to decadal climate variability from oceanographic data, coral records and model simulations
M. Rhein, G. Lohmann, J. Pätzold
T. Felis, M. Ionita, M. Kölling, H. Kuhnert, C. Mertens, S. Mulitza, P. Scholz, M. Segl, A. Ströh, M. Werner, H. Wu
Climate variability modes and their teleconnections are evaluated for the instrumental period and the Holocene, using new oceanographic data, climate modeling and proxy data from corals. The Project combines former Project A7 (Decadal climate variability from high-resolution marine archives and model simulations) and Cluster of Excellence Project A11 (Variability of deep-water formation in the North Atlantic).
The Project aims at quantifying the full range of natural climate variations on seasonal to (multi-) decadal timescales. Climate change on these timescales is evident through phenomena such as the North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation (ENSO) and the monsoons, contributing to climate extremes and socioeconomic hardship throughout the globe. The response of these natural modes of climate variability to greenhouse warming plays a crucial role in model projections of future climate. However, climate variability on these timescales is poorly understood with respect to its behavior prior to the period of instrumental observations, restricting our knowledge on the interactions of climate modes and the stability of their teleconnections.
Oceanographic and historical observations in the North Atlantic Ocean are investigated to decipher its role in controlling and mediating climate variability on these timescales. A combination of long-term hydrographic data and model simulations allowed to estimate past and future trends of the Atlantic meridional overturning circulation (Lohmann et al., 2008). Winter and summer blocking variability in the North Atlantic region was investigated using long-term observational and proxy data from southwestern Greenland (Rimbu & Lohmann, 2011). Summer drought variability over Europe and its relationship to global sea surface temperature was investigated during the observational period, providing a potential for predicting drought conditions on interannual to decadal timescales (Ionita et al., 2011).
Annually-banded reef corals are used to generate sub-seasonally resolved proxy records of temperature, salinity and hydrologic balance at the sea surface. A coral record from the Kuroshio recirculation region revealed an abrupt early 20th century freshening in the western North Pacific (Felis et al., 2009) not deducible from the short instrumental record, and a prominent PDO control on regional winter temperatures since AD 1873, highlighting a potential for marine PDO reconstructions further back in time (Felis et al., 2010). Ongoing work on northern Red Sea coral records provided further evidence for a prominent control of NAO atmospheric teleconnections on eastern Mediterranean/Middle East climate on seasonal and interannual to decadal timescales, using a combination of proxy records, gridded instrumental climate data and model simulations (Felis et al., 2004, Rimbu et al., 2006, Felis & Rimbu, 2010). A new MARUM Fellowship and Incentive Funds Project provides seasonally resolved climate information from Caribbean coral records for the period of the demise of the Maya Civilization (AD 750-1050), which according to lower resolution proxy records was accompanied by severe drought cycles.
Figure 1.
Left: Sea-surface salinity map of the North Pacific Ocean (Conkright et al., 2002). The coral site in the Ogasawara Islands and schematic flow patterns of Kuroshio, Kuroshio Extension, and Kuroshio recirculation are shown. X-radiographs of the Porites coral core. Alternating bands of high (dark colour) and low skeletal density (light colour) are visible. A high-density (summer)/low-density (winter) band pair represents one year. Corresponding years of coral growth are indicated. Core length: 1.74 m, core diameter: 5.5 cm.
Right: Interannual record of paleosalinity from a western subtropical North Pacific coral. Instrumental sea surface salinity (SSS) axis is visually scaled. Thin lines—annual records and corresponding error bars; bold lines—three-year running averages; gray bar—time interval 1905–1910. Residual coral δ18O records (Δδ18O) based on δ18O and Sr/Ca, and δ18O and U/Ca; coral-based SSS anomaly calculated from regional δ18Oseawater- salinity relationship (0.42‰ per 1 psu) (Schmidt et al., 1999); and regional SSS from Simple Ocean Data Assimilation (SODA) reanalysis (Carton and Giese, 2008) (27.0°–27.5° N, 142.0°–142.5° E). Fram Strait sea-ice export reconstruction (Schmith and Hansen, 2003).
Felis, T, Suzuki, A, Kuhnert, H, Dima, M, Lohmann, G, Kawahata, H (2009) Subtropical coral reveals abrupt early-twentieth-century freshening in the western North Pacific Ocean. Geology, 37, 527-530 Reprint