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Introduction Ocean fronts are moving ephemeral biological hotspots forming at the interface of cooler and warmer waters. In the open ocean, this is where marine organisms, ranging from plankton to mesopelagic fish up to megafauna, gather and where most fishing activities concentrate. Fronts are critical ecosystems so that understanding their spatio-temporal variability is essential not only for conservation goals but also to ensure sustainable fisheries. The Mozambique Channel (MC) is an ideal laboratory to study ocean front variability due to its energetic flow at sub-to-mesoscales, its high biodiversity and the currently debated conservation initiatives. Meanwhile, fronts detection relying solely on remotely-sensed Sea Surface Temperature (SST) cannot access aspects of the subsurface frontal activity that may be relevant for understanding ecosystem dynamics. Method In this study, we used the Belkin and O’Reilly Algorithm on remotely-sensed SST and hindcasts of a high-resolution nested ocean model to investigate the spatial and seasonal variability of temperature fronts at different depths in the MC. Results We find that the seasonally varying spatial patterns of frontal activity can be interpreted as resulting from main features of the mean circulation in the MC region. In particular, horizontally, temperature fronts are intense and frequent along continental shelves, in islands’ wakes, at the edge of eddies, and in the pathways of both North-East Madagascar Current (NEMC) and South-East Madagascar Current (SEMC). In austral summer, thermal fronts in the MC are mainly associated with the Angoche upwelling and seasonal variability of the Mozambique current. In austral winter, thermal fronts in the MC are more intense when the NEMC and the Seychelles-Chagos and South Madagascar upwelling cells intensify. Vertically, the intensity of temperature fronts peaks in the vicinity of the mean thermocline. Discussion Considering the marked seasonality of frontal activity evidenced here and the dynamical connections of the MC circulation with equatorial variability, our study calls for addressing longer timescales of variability to investigate how ocean ecosystem/front interactions will evolve with climate change.
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This content will become publicly available on January 1, 2026
A New Robust Frontal Disturbance Index of the Oyashio Extension Sea Surface Temperature Front
Abstract The Oyashio Extension (OE) frontal zone in the northwest Pacific Ocean is associated with strong gradients of sea surface temperature (SST) and salinity. The OE front enhances baroclinicity and anchors the storm tracks; changes in its position and strength may impact atmospheric variability. North–south shifts in the OE front are often defined using the leading principal component for the latitude of the absolute maximum SST gradient in the northwest Pacific (145°–170°E), the so-called Oyashio Extension index (OEI). We show that the OEI is sensitive to the choice of SST dataset used in its construction, and that the significance of regressions of atmospheric fields onto the OEI also depends on the choice of SST datasets, leading to nonrobust results. This sensitivity primarily stems from the longitudinal domain used to define the OEI including a region with parallel or indistinct frontal zones in its central section (155°–164°E), leading to divergent results across datasets. We introduce a new index that considers the extent to which the SST front across this central section departs from climatology, the frontal disturbance index (FDI). For the months considered and over short time lags, the FDI produces more consistent results on air–sea interactions and associated high-frequency storm-track metrics than the conventional OEI, with a southward shift of the storm track for a more positive FDI. The FDI appears to be related to oceanic mesoscale eddy activity in the central OE region. There are significant asymmetric associations between the FDI and storm-track metrics dependent on the sign of the FDI. Significance StatementIn this study, we aim to understand how the choice of dataset may influence the interpretation of interactions between the ocean and the overlying atmosphere near sea surface temperature (SST) fronts. We find that using different SST datasets affects the results, due to slight differences in the representation of the location of the maximum SST gradient. To understand this, we develop a new index which relates to the degree of disturbance of the SST front. The new index produces regression results that are more consistent across the different datasets. We also identify some possible links between the frontal disturbance and the presence of ocean eddies. We advise that the sensitivity to dataset choice is given due consideration in regions near SST fronts.
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- Award ID(s):
- 2040073
- PAR ID:
- 10567652
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 38
- Issue:
- 1
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 293 to 307
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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