Seasonal variability of the net water-mass transport among the four major basins

<p>Global water cycle involves water-mass transport on land, atmosphere, ocean, and among them. Quantification of such transport, and especially its time evolution, is essential to identify footprints of the climate change and helps to constrain and improve climatic models. In the ocean, net water-mass transport among the ocean basins is a key, but poorly estimated parameter presently. We propose a new methodology that incorporates the time-variable gravity observations from the GRACE satellite (2003-2016) to estimate the change of water content, and that overcomes some fundamental limitations of existing approaches. We show that the Pacific and Arctic Oceans receive an average of 1916 (95% confidence interval [1812, 2021]) Gt/month (~0.72 ± 0.02 Sv) of excess freshwater from the atmosphere and the continents that gets discharged into the Atlantic and Indian Oceans, where net evaporation minus precipitation returns the water to complete the cycle. This salty water-mass transport from the Pacific and Arctic Oceans to the Atlantic and Indian Oceans show a clear seasonal variability, with a maximum transport of 3000 Gt/month during boreal summer, a minimum of 1000 Gt/month or less on February, Mars, and November.</p><p>This research has been primarily supported by the Spanish Ministerio de Ciencia, Innovación and Universidades research project DEEP-MAPS (RTI2018-093874-B-I00).</p>

Water transport among the world ocean basins within the water cycle

The global water cycle involves water-mass transport on land, in the atmosphere, in the ocean, and among them. Quantification of such transport, especially its time evolution, is essential to identify the footprints of climate change, and it also helps to constrain and improve climatic models. In the ocean, net water-mass transport among the ocean basins is a key process, but it is currently a poorly estimated parameter. We propose a new methodology that incorporates the time-variable gravity observations from the Gravity Recovery and Climate Experiment (GRACE) satellite (2003–2016) to estimate the change in water content; this new approach also overcomes some fundamental limitations of existing methods. We show that the Pacific and Arctic oceans receive an average of 1916 (95 % confidence interval of [1812, 2021]) Gt per month (∼0.72±0.02 Sv) of excess freshwater from the atmosphere and the continents that is discharged into the Atlantic and Indian oceans, where net evaporation minus precipitation returns the water to complete the cycle. This is in contrast to previous GRACE-based studies, where the notion of a see-saw mass exchange between the Pacific and the Atlantic and Indian oceans has been reported. Seasonal climatology as well as the interannual variability of water-mass transport are also reported.

Water transport among the world ocean basins within the water cycle

Global water cycle involves water-mass transport on land, atmosphere, ocean, and among them. Quantification of such transport, and especially its time evolution, is essential to identify footprints of the climate change and helps to constrain and improve climatic models. In the ocean, net water-mass transport among the ocean basins is a key, but poorly estimated parameter presently. We propose a new methodology that incorporates the time-variable gravity observations from the GRACE satellite (2003–2016) to estimate the change of water content, and that overcomes some fundamental limitations of existing approaches. We show that the Pacific and Arctic Oceans receive an average of 1916 (95 % confidence interval [1812, 2021] Gt/month (~0.72 ± 0.02 Sv) of excess freshwater from the atmosphere and the continents that gets discharged into the Atlantic and Indian Oceans, where net evaporation minus precipitation returns the water to complete the cycle. This is in contrast to previous GRACE-based studies, where the notion of a seesaw mass exchange between the Pacific and Atlantic/Indian Oceans has been reported. Seasonal climatology as well as the interannual variability of water-mass transport are also reported.

TRACKING THE ORIGIN OF MOISTURE OVER SERBIA USING THE LAGRANGIAN METHOD

In this study, we investigate the sources of moisture over Serbia using a Lagrangian method based on the FLEXPART V9.0 particle dispersion model combined with ERA-Interim reanalysis data, to track changes in atmospheric moisture. This approach computes the budget of evaporation-minus-precipitation by calculating changes in specific humidity along forward and backward trajectories. We considered a period of 34 years, from 1980 to 2014, which allowed the identification of climatological moisture sources and moisture transport towards the country. The results showed that Serbia receive moisture mainly from two sources: the Mediterranean Sea which is the dominant source during the winter (October-March) and the own region which predominate during the summer (April-September). Key words: moisture sources, Flexpart, Lagrangian method, Serbia

Satellite- and Reanalysis-Based Mass Balance Estimates of Global Continental Discharge (1993–2015)

Total continental freshwater discharge into the oceans is a key feature of the global water cycle, but it is currently impossible to observe using ground-based methods alone. To characterize the uncertainty across existing modeling and satellite approaches, the authors present ensembles of historic monthly global continental discharge estimates that enforce water mass balance over land and ocean. The authors combine independent measurements of ocean–landmass change from altimetry and GRACE with multiple estimates of evaporation minus precipitation ( E − P) from remote sensing and reanalysis data to compute 28 time series of global discharge. Results reveal agreement in mass budget across approaches but a large spread in global E − P estimates that propagates into the discharge estimates. It is found that discharges with reanalysis-based E − P provide a closer comparison with current observation-based estimates. After combining GRACE- and altimetry-based mass change estimates with moisture convergences from reanalysis, the total annual mean continental discharge into the oceans is 38 550 ± 4800 km3 yr−1. Last, the authors provide continent-wise discharge estimates from GRACE and moisture convergences over land, compare them to other studies, and discuss implications for ocean modeling.

A Lagrangian analysis of the present-day sources of moisture for major ice-core sites

A Lagrangian approach was used to identify the moisture sources for 14 ice-core sites located worldwide for the period of 1980–2012. The sites were classified into three domains: Arctic, Central (Andes, Alps, and Kilimanjaro), and Antarctic. The approach was used to compute budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day backward trajectories. The results indicate that the oceanic regions around the subtropical high-pressure centres provide most of moisture, and their contribution varies throughout the year following the annual cycles of the centres. For the Arctic Domain, the sources lie in the subtropical North Atlantic and Pacific. The subtropical South Atlantic, Indian, and Pacific oceans provide moisture for the Antarctic Domain. The sources for South America are the Atlantic and South Pacific, for Europe the sources are in the Mediterranean and the North Atlantic, and for Asia the sources are the Indian Ocean and the Arabian Sea.

A Lagrangian analysis of the present-day sources of moisture for major ice-core sites

A Lagrangian approach was used to identify the moisture sources for fourteen ice-core sites located worldwide for the period 1980–2012. The sites were classified into three domains: Arctic, Central (Andes, Alps and Kilimanjaro), and Antarctic. The approach was used to compute budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day backward trajectories. The results indicate that the oceanic regions around the subtropical high-pressure centers provide most of moisture, and their contribution varies throughout the year following the annual cycles of the centers. For the Arctic domain, the sources lie in the subtropical North Atlantic and Pacific. The subtropical south Atlantic, Indian and Pacific provide moisture for the Antarctic domain. The sources for South America are the Atlantic and southern Pacific, for Europe the sources are in the Mediterranean and the north Atlantic, and for Asia the sources are the Indian Ocean and the Arabian Sea.

Centennial Changes of the Global Water Cycle in CMIP5 Models

The global water cycle is predicted to intensify under various greenhouse gas emissions scenarios. Here the nature and strength of the expected changes for the ocean in the coming century are assessed by examining the output of several CMIP5 model runs for the periods 1990–2000 and 2090–2100 and comparing them to a dataset built from modern observations. Key elements of the water cycle, such as the atmospheric vapor transport, the evaporation minus precipitation over the ocean, and the surface salinity, show significant changes over the coming century. The intensification of the water cycle leads to increased salinity contrasts in the ocean, both within and between basins. Regional projections for several areas important to large-scale ocean circulation are presented, including the export of atmospheric moisture across the tropical Americas from Atlantic to Pacific Ocean, the freshwater gain of high-latitude deep water formation sites, and the basin averaged evaporation minus precipitation with implications for interbasin mass transports.