Altimetric Studies of the Oceanic Pathways in the Northeast Pacific Ocean

Author:

Paul Strub - (Oregon State University)

Co-Investigator(s):

Melanie Fewings (Oregon State University)
Ricardo Matano (Oregon State University)

Abstract:

OBJECTIVES: Using 28+ years of satellite altimeter data, complemented by high-resolution ocean circulation models, we will characterize and quantify transports and pathways of water parcels along the eastern North Pacific margin between Mexico and Canada (in the 'Oceanic Pathway' from the eastern equatorial Pacific to the Alaska Gyre).

We will focus on pathways surrounding and within the ecologically and economically important equatorward California Current System (CCS, 23°-48°N) during (1) average seasonal cycles and (2) periods of strong anomalies in the circulation on interannual time scales, including warm and cool extremes of the El Niño/Southern Oscillation (ENSO) cycle and recent marine heat waves (MHWs). This pathway is often invoked to explain anomalous appearances in the CCS of more tropical water masses and warm-water species of plankton during El Niños, although estimates of actual transports and water displacements are poorly known. We will quantify the changes in advection into and out of the northern and southern boundaries of the CCS during average seasonal cycles, extremes of the ENSO cycle (both warm and cool) and over other anomalous periods, such as the recent, repeated MHWs.

METHODS: We will use combinations of satellite altimeter, wind, and sea-surface temperature (SST) data, along with high-resolution ocean circulation models, to quantify the annual and interannual variability in the Eulerian velocities and transports (surface and subsurface) and Lagrangian water parcel trajectories during 1993-2020+. To form the total geostrophic velocities needed for the Lagrangian calculations, we require a long-term mean velocity field. The averaged model fields will be used to evaluate the available Mean Dynamic Topography (MDT) velocity fields for this use and provide an alternative mean velocity field, which we have found necessary in previous calculations. Model fields will also extend the altimeter velocities and displacements to the full water column and clarify the dynamics that govern the variability in the circulation along the Oceanic Pathway. Consistency between the altimeter and model results will help validate both.

IMPACT – RELEVANCE TO NASA: The assumption that the Oceanic Pathway is an efficient avenue for poleward water parcel and plankton transports over long distances has been used by biologists for the past 40 years. We will test that assumption. Clarification of Lagrangian trajectories from altimeter fields along the Oceanic Pathways will improve our understanding of the large-scale oceanographic circulation, relevant to interannual climate variability (Research Theme #1 of the NASA OST solicitation). At locations along the Oceanic Pathway, the arrival of anomalous water properties and species affects the coastal physical and ecosystem dynamics (Research Theme #2). We will also evaluate the ability of altimeter-based climate indexes to characterize the displacements along the Oceanic Pathway, which can be used as indicators and, on some time scales, predictors of the arrival of distant water properties and species that may affect local ecosystems and fisheries (Research Theme #4). The fields from the model runs will also available for use by the large community of scientists working in the CCS ecosystem. The proposed work is relevant and timely due to the recent strong El Niño and MHWs. Our team includes complementary expertise in altimeter data analysis and El Niño effects on coastal upwelling systems (Strub, James), high-resolution coastal modeling (Matano, Combes), and midlatitude MHWs in coastal regions (Fewings). Together, we will determine the effectiveness of the purported Oceanic Pathway in transporting water masses that cause ecosystem disruptions, including $100Ms per year of damage to economically important fisheries, along the US West Coast. The techniques we develop here will be applicable to future studies in coastal regions and along other eastern ocean boundaries globally.

Altimetric Studies of the Oceanic Pathways in the Northeast Pacific Ocean — The “Oceanic Pathway” as well documented for SSH signals mov-ing from the equator to the tropics to the midlatitudes in the NE Pa-cific. How far are water properties and passive plankton populations transported along segments of this pathway during ‘normal’ seasonal cycles, ENSO phases and Marine Heat Waves? Emphasis is on the region from Mexico to Canada.

Supported by NASA