Climatology of surface chlorophyll a, autumn‐winter and spring blooms in the southwest Pacific Ocean

Abstract

[1] Ocean color data from the 13 year Sea-viewing Wide Field-of-view Sensor mission are used to examine the distribution of surface chlorophyll a in the southwest Pacific Ocean. The mean surface chlorophyll field is similar to that found by previous workers, with elevated levels in the Subtropical Front and around the subantarctic islands that have an associated shelf. The annual cycle in surface chlorophyll shows a ubiquitous summer bloom in subantarctic water, with autumn, winter, and spring blooms variously in subtropical water and across the Subtropical Front. The autumn blooms progress equatorward with time at the same rate as wind stress. This supports the idea that the autumn bloom develops in response to increased wind stress, with a likely mechanism for the bloom being mixing to the surface of the deep chlorophyll maximum, and/or increased production due to entrainment of nutrients. The spring bloom progresses poleward with time. It starts after the mixed layer reaches its deepest, and its timing appears to be linked to the reduction in wind stress in spring. Under the assumption that all tracers are well mixed to the seasonal thermocline in autumn and winter, we conclude that vertically integrated chlorophyll increases at all latitudes in subtropical water during autumn and winter. Unfortunately, carbon-to-chlorophyll ratios are not known well enough to determine whether the same is true for vertically integrated carbon biomass. Individual spring blooms show significant spatial structure and are different from year to year. This leads to low spatial coherence for the temporal variability in surface chlorophyll.

Decoupling Between Phytoplankton Growth and Microzooplankton Grazing Enhances Productivity in Subantarctic Waters on Campbell Plateau, Southeast of New Zealand

“…The range of chl a concentrations measured in autumn on the C. Plateau (Table ) was in good agreement with previous in situ measurements made on the plateau (0.25–2.00 mg m −3 ) (Heath & Bradford‐Grieve, ) and in SAW east of New Zealand (0.2–0.4 mg m −3 ) (Boyd et al, 1999, Boyd et al, ; Bradford‐Grieve et al, ; Gall et al, ). The high variability (0.1 to >1.5 mg m −3 ) observed on the plateau was consistent with the patchy distributions of chl a observed by satellite data, with elevated levels associated with the Auckland and Campbell islands and the Pukaki Rise in this (Figures and S6) and previous studies (Chiswell et al, ; Heath & Bradford‐Grieve, ; Pinkerton, ).…”

“…In the present study, we argue that the erosion of the thermocline and changes in the MLD represents the perturbations that disrupt the equilibrium within the HNLC microbial system. In line with this interpretation we found a positive, although not significant, relationship between phytoplankton growth rate and the depth of the mixed layer across all regions (R‐Spearman = 0.41, n = 10) (Figures a and S5) that reflects to some extent the phytoplankton response to the vertical entrainment of subsurface nutrients caused by the thermal and wind‐driven erosion of the summer pycnocline (Chiswell et al, ) (Figure S1d). This positive trend suggests that phytoplankton physiology was able to cope with decreasing light exposure associated with the deepening mixed layers without severely compromising their growth.…”

Vertical Mixing Effects on Phytoplankton Dynamics and Organic Carbon Export in the Western Mediterranean Sea

“…The first event deepened the mixed layer down to the DCM, and the second brought it below the nutricline. This sequence of events, which began with the mixing of the DCM, followed by an increase of primary production caused by the nutrient supply from deeper layers, induced by increased wind stress, has been previously described by Chiswell et al (). Lavigne et al () indicated that DCM erosion could explain 60% of chlorophyll profiles observed in the Ionian region in December and January.…”

Spring bloom dynamics and zooplankton biomass response on the US Northeast Continental Shelf

“…The relative stability of bloom dynamics suggested by climatological patterns is in contrast to the variability observed spatially and temporally within ecosystems. Regional analyses often reveal complex patterns of meso- scale heterogeneity in bloom dynamics often related to features of the underlying physical environment (Zhao et al, 2013), the physiochemical regime of the ecosystem (Shiozaki et al, 2014), or inter-annual variability of the wind regime (Chiswell et al, 2013;Navarro et al, 2012). However, broad-scale climate dynamics such as the North Atlantic Oscillation (Zhai et al, 2013) and El Nino/ Southern Oscillation (D'Ortenzio et al, 2012) can influence coherent patterns of bloom dynamics.…”