Ocean-induced melt triggers glacier retreat in Northwest Greenland
In recent decades, tidewater glaciers in Northwest Greenland have contributed significantly to sea level rise but have also exhibited a complex spatial pattern of retreat that remained unexplained. In this new study, NASA's Oceans Melting Greenland (OMG) data is used in combination with ECCO model outputs to assess the role of the ocean in triggering the retreat of these glaciers. The timing of glacier retreat coincides with the timing of increased ocean‐induced melting of the ice faces above average, which is driven by increases in ocean temperature and surface melt. While glacier retreat is initiated by the ocean, the calving of icebergs remains the dominant process of mass loss at the ice fronts (71%). The speed of retreat varies strongly with the slope of the glacier bed: fast retreats occur in deep fjords exposed to warm water and slow retreats in shallow fjords with cold water. These results highlight the dominant role of ice‐ocean interactions on the mass balance of the Greenland ice sheet.
Wood, M., Rignot, E., Fenty, I., Menemenlis, D., Millan, R., Morlighem, M., Mouginot, J. & Seroussi, H. (2018). Ocean‐induced melt triggers glacier retreat in Northwest Greenland. Geophysical Research Letters, 45(16), 8334-8342. doi: 10.1029/2018GL078024
A New 20-year Ocean Climatology
A new 20-year ocean climatology has been created for ocean circulation and climate studies based on the recent ECCO version 4 release 3 ocean state estimate. In comparison to conventional climatologies based on observations alone, the new ECCO climatology accounts for the very great inhomogeneity with which the ocean has been observed. The new climatology includes all conventional variables of a general circulation model over the entire water column and is consistent with the diversity of data available from the global observation system. All basic convservation rules for ocean circulation, including enthalpy and energy, are obeyed to machine precision in the model equations.
Mechanisms of the recent decadal trend of the North Atlantic Ocean heat content
The subpolar North Atlantic (SPNA) reversed trends in ocean heat content from warming during 1994–2004 to cooling over 2005–2015. ECCO V4r3 reveals that this reversal is the result of anomalous horizontal midlatitude gyre circulation acting on the mean temperature gradient, rather than changes in overturning circulation. Results have implications for decadal predictability.
Piecuch, C. G., R. M. Ponte, C. M. Little, M. W. Buckley, and I. Fukumori (2017), Mechanisms underlying recent decadal changes in subpolar North Atlantic Ocean heat content, Journal of Geophysical Research: Oceans, 122(9), 7181-7197, doi:10.1002/2017JC012845.
Coherent Arctic Ocean Bottom Pressure Variations
Across the Arctic Ocean and the Nordic Seas, GRACE and in-situ observations identified a basin-wide mode of ocean bottom pressure and sea-level fluctuation with spatially near-uniform amplitude and phase. This basin-wide fluctuation is barotropic and dominates the region’s large-scale variability from sub-monthly to interannual timescales. Using ECCO v4 and its adjoint, the source of these coherent ocean bottom pressure variations were identified as being coastally-trapped waves generated by winds along the continental slopes of the Arctic Mediterranean and its neighboring seas including the North Atlantic Ocean. Winds drive Ekman transport across the large bathymetric gradients, forcing mass divergence between the shallow coastal area and the deep ocean basins and creating ocean bottom pressure anomalies of opposite signs in the two regions. The resulting propagation and mutual interaction of these waves gives rises to the observed pressure anomalies. This study illustrates the utility of using the model’s adjoint for identifying causal mechanisms underlying a complex system
I. Fukumori, O. Wang, W. Llovel, I. Fenty and G. Forget, 2015: A near-uniform fluctuation of ocean bottom pressure and sea level across the deep ocean basins of the Arctic Ocean and the Nordic Seas. Prog. Oceanogr., 134, 152-172, doi:10.1016/j.pocean.2015.01.013