Variability of fine-scale chlorophyll fronts in the Tīpaka Moana Te
Moana Nui a Toi Hauraki Gulf, Aotearoa New Zealand
Abstract
Aotearoa New Zealand’s marine environment is heavily impacted by El Niño
Southern Oscillation (ENSO). Little is known about the effect of ENSO on
oceanographic properties in the area or their consequences on the
distribution of marine organisms. Here we characterise the
spatio-temporal variability of fine-scale fronts (< 10 km) in
the area of Tīpaka Moana Te Moana Nui a Toi Hauraki Gulf (HG) and
investigate the impact of dominant wind direction, seasonality, and ENSO
phase. We processed Ocean-Land Color Instrument (OLCI) images from
satellites between 2016-2022 with a fit-for-purpose version of the
Belkin and O’Reilly Algorithm, specifically for frontal detection. We
find coherent shifts in the position of fine-scale features, with ENSO
phases alternatively separate and connect different parts of the Gulf
during El Niño and La Niña respectively. Overall, fronts tend to
co-locate with the 70 m and 40 m isobaths in the outer and inner HG
respectively and their locations shift close or away from shore in
response to changes in dominant wind direction. Furthermore, offshore
fronts occurrences increase during winter and spring, and nearshore ones
increase during summer and autumn. Our results sketch a first assessment
of the distribution of fine-scale features that are likely to impact the
distribution of important areas for pollutants dispersion and feeding
areas for marine megafauna.