The Seasonality of Global Land and Ocean Mass and the Changing Water Cycle

Abstract

The global water cycle is generally viewed as the cycling of water masses among the land, ocean, and atmosphere. This cycling predominantly occurs at the annual time scale and between land and ocean, constituting the seasonal global water cycle. NASA’s Gravity Recovery and Climate Experiment (GRACE) and GRACE‐Follow On missions can directly observe the seasonal global water cycle and describe the changes in its intensity. We present seasonal amplitudes of the global land water and ocean mass anomalies between 04/2002 and 11/2020. We find that the average seasonal amplitude is 17.0 ± 0.6 mm sea level equivalent (SLE), and its interannual variability (σ = 1.1 mm SLE) is comparable to the long‐term trends in the land and ocean masses. We investigate two periods of rapid amplification and deamplification during which the amplitude changed as much as 29%, and find that changes in hydroclimatology in certain land regions modulate the seasonal global water cycle.

Global Ocean Salinity Measurements Have Some Serious Issues After 2015

“…While most of the Argo-based salinity products indicate a significant salinification in the upper ocean during 2015-2019, salinity inferred from GRACE/GRACE-FO data shows a very small negative trend (-0.2 × 10 -4 g/kg/yr) and in line with prior two periods, although there is evidence of small instrument errors post 2015 based on sea level budget studies 12 . In contrast, the smallest estimate from the Argo-based salinity products over 2015-2019 is from SIO at 0.7 × 10 -4 g/kg/yr, which is also the only estimate that is not significantly different from 0 (2σ uncertainty at 2.4 × 10 -4 g/kg/yr).…”

“…The observed discrepancy between independent estimates brings into question the reliability of the Argo-based ocean salinity products after 2015, and challenges our understanding of how mean ocean salinity should change in the presence of enormous fluxes of fresh water into the ocean from ice sheets and glaciers and only small changes in global land water storage 11,12,13 .…”

Geological carbon cycle constraints on the terrestrial hydrological response to higher atmospheric CO₂

“…Critically, our long-term perspective on the runoff response to CO2 incorporates a number of processes that are thought to affect q but are difficult to constrain in the modern due to temporally limited instrumental records or experiments. For example, remotely sensed products of global discharge are affected by internal variability, which precludes their use currently in assessing how total runoff will respond to rising atmospheric CO2 (Chandanpurkar et al, 2017(Chandanpurkar et al, , 2021. Experiments that seek to understand how plant responses might affect runoff-such as the Free Air CO2 Enrichment (FACE) experiments-are relatively short-term and the long-term response of ecosystems may differ from the short-term response due to changes in nutrient demands and supply and nonlinear plant responses to increasing CO2.…”

Amplitude modulations of seasonal variability in the Karimata Strait throughflow

“…The 2year window is selected because it can maintain a better continuity of results and show subtle changes in the annual cycle, while minimizing the interference of high-frequency changes (Hamlington et al, 2019). The fitting step involves solving the least squares function to obtain the optimal linear trend and annual harmonics (Chandanpurkar et al, 2021). The value obtained from each fitting is assigned to the intermediate time.…”

“…The time interval of seasonal amplitude time series by this method is one month. The seasonal amplitude is defined as half of the difference between peak and trough, which is half of that from Chandanpurkar et al (2021).…”