Spatial and seasonal variability of horizontal temperature fronts in the Mozambique Channel for both epipelagic and mesopelagic realms

Abstract

IntroductionOcean 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.MethodIn 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.ResultsWe 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.DiscussionConsidering 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.

East Australian Current System: Frontal Barrier and Fine‐Scale Control of Chlorophyll‐a Distribution

“…Moreover, fronts are not confined at the surface and can extend below the mixed-layer (Siegelman et al, 2020). For example, research by Sudre et al (2023) in the Mozambique channel demonstrates that frontal dynamics below the surface significantly differ from those observed at the surface, and these subsurface fronts are important in regards to biological hotspots. They notably observed that the intensity of temperature fronts peaks below the mixed layer.…”

Implementation of the Pelagic Hotspot Index in detecting the habitat suitability area for bigeye tuna (Thunnus obesus) in the eastern Indian Ocean

“…We align with these as the results coincide with Cai et al (2020), which observed that the high tuna catch area was in a sub-ST front ranging from 150-200 m. We also indicate that the fronts occurring within the study area are significantly influenced by the current systems operating in the water column. A study conducted by Sudre et al (2023) states that the front peaks between 100 and 200 meters below the mixed layer suggest that they are primarily related to features of ocean dynamics rather than to mixed layer processes.…”