Collaborative Research: An analysis of 150 years of sea surface and subsurface observations to map whole-ocean temperature and detect circulation change

Harvard University, Cambridge MA

Investigators

Abstract

In this project, surface and subsurface observations of ocean temperature will be combined with a numerical model of the ocean circulation to optimally estimate changes in ocean temperature and heat uptake over the past 150 years. Ocean heat uptake is a critical quantity for understanding the degree to which the Earth’s climate is out of energetic equilibrium and for purposes of constraining equilibrium warming in response to increases in greenhouse gases. This integrated analysis will allow testing for the presence of systematic errors in ocean temperature observations and to examine whether and how ocean circulation has varied over the last 150 years. Products of the research will include a quality-controlled dataset of ocean temperature observations and a corresponding time-evolving, three- dimensional mapping over the modern warming era. Sea surface and subsurface ocean temperature observations will be combined with an inverse ocean-circulation model to constrain temperature and ocean heat uptake over the last 150 years. Historical subsurface temperature observations will be used to evaluate random and systematic errors within and across data sets. This examination will leverage both a linear-mixed-effects methodology previously developed by the investigators and applied to identify offsets among sea-surface temperature observations, as well as a data-constrained circulation model also previously developed by the investigators and applied for purposes of inter-comparing interior and surface boundary properties. An existing circulation estimate, conditioned on modern tracers, will be used to test for changes in ocean circulation over the last 150 years. A three-dimensional mapping of ocean temperatures over the last 150 years that combines constraints from surface and interior ocean observations will be produced. The mapping will make use of the data-constrained circulation model and will be performed repeatedly in order to develop multiple ensembles that capture uncertainties associated with random and systematic observational errors, as well as uncertainties in circulation and initial conditions. Integration over this temperature mapping will provide estimates of ocean heat uptake and associated uncertainties. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.