CoAuthors

Gregory Johnson (NOAA/PMEL, United States)

Global mean sea level has been rising rapidly and steadily over recent decades, but regional sea level trends can be quite variable and often of larger magnitude. These regional trends are important to investigate since they are more closely tied to changes in inundation risk faced by coastal communities. Sea level changes are driven by a number of processes that include changes to the density and mass of the ocean. We can measure the density (i.e., steric) changes using Argo floats and the mass (i.e., barystatic) changes using gravimetry measurements from GRACE/GRACE-FO. To assess the performance of these measurement systems in capturing these contributions to sea level change and to better understand the underlying processes being measured, we can compare the sum of the steric and barystatic changes to independent, altimeter-based sea level anomalies to see if the sea level budget (SLB) “closes”. In this work, we build off of previous Argo/GRACE/altimetry studies by explicitly calculating the deep ocean steric contribution from an array of Deep Argo floats in the Southwest Pacific Basin. Previous work estimated this contribution from decadal hydrographic surveys but had difficulty closing the SLB in this region without the higher temporal and spatial resolution of the deep steric term from Deep Argo. We analyze the SLB within 6° × 6° grid cells that are equivalent in size to four GRACE/GRACE-FO mascons and similar in scale to the ~5° × 5° target resolution of the Deep Argo array. Grid cell averages of the upper and deep ocean steric terms are constructed using all available Core and Deep Argo profiles, instead of estimating these values from a climatology as often done in previous work. GRACE/GRACE-FO data are combined across the four individual mascons that make up each grid cell and grid cell averages of the along-track sea level anomaly measurements (from the NOAA/EUMETSAT Radar Altimeter Database System) are calculated by applying a Gaussian convolution averaging kernel to all available altimeter passes over each grid cell. Over the lifetime of the Southwest Pacific Basin Deep Argo array (January 2016–present), we compare the trend in the sea level anomaly to the trends in the barystatic and steric sea level terms to assess the impact of the Deep Argo data on the closure of the SLB over 6° × 6° regions in this basin.