Ocean color variability in the Tasman Sea

Abstract

The Tasman Sea contains the largest noncoastal surface chlorophyll‐a concentrations within the South Pacific Ocean. Observations of ocean color from SeaWiFS demonstrate that the chlorophyll‐a seasonal cycle is characterized by a large austral spring bloom and a much smaller fall bloom separated by periods of lower concentrations, typical of communities within the North Atlantic Ocean. However, the seasonal cycle of the mixed layer depth of the Tasman Sea is much more similar to the North Pacific Ocean, whose persistent winter stratification results in relatively constant chloropohyll‐a concentrations. Examination of eddy kinetic energy from satellite altimetry (TOPEX/Poseidon and ERS‐2 blended product) reveals that the western Tasman Sea contains a large number of eddies originating within the East Australian Current that coincide spatially with the blooms. Upwelling and downwelling associated with these eddies greatly increase vertical mixing within the upper ocean, offsetting the normally shallow winter mixed layer, which leads to a chlorophyll‐a seasonal cycle much like that of the North Atlantic Ocean.

Remote sensing of coccolithophore blooms in selected oceanic regions using the PhytoDOAS method applied to hyper-spectral satellite data

“…10 left panel), coccolithophores grew negligibly in nAtl and chl-a decreased in the two southern regions by different rates; total chl-a increased in all regions; PIC decreased strongly in nAtl and sAtl, while it strongly increased in sPac. This may have been caused by the strong SST-rise in the Tasman Sea (Tilburg et al, 2002), even though this SST rise was not observed in our sPac simple trend; however, the decreasing rate of SST in sAtl and sPac was clearly followed consistently by the decrease of coccolithophores; and the rate of increase of SST in nAtl was associated, at a small rate, with the increase of coccolithophores. The surface wind-speed decreased in nAtl is dominated by diatoms and the Weddell Sea has abundant coccolithophores, there are other studies (e.g.…”

“…Moreover, large eddies occurring in the Tasman Sea have a great contribution to the vertical mixing within the upper ocean. This increased mixing effectively counteracts the winter stratification and results in a varying chl-a seasonal cycle (Tilburg et al, 2002). In this sense, the seasonal cycle of chl-a in sPac should be pronounced, similar to the North Atlantic, which has very strong mixing.…”

“…In the same context, increased oceanic CO 2 , which is a response to the increase in atmospheric CO 2 (anthropogenic contribution), affects the rate of calcification by coccolithophores by reducing the supersaturation state of the carbonate ion (Riebesell et al, 2000). Moreover, sinking through the water column and getting deposited in the sediment (either directly as coccoliths and detritus or after being converted into PIC), coccolithophores are considered to be one of the main drivers of the biological carbon pump (Raven and Falkowski, 1999;Rost and Riebesell, 2004;Thierstein and Young, 2004) and hence a key component of the global carbon cycle (Westbroek et al, 1993). Coccolithophores are known for frequently forming large-scale blooms, where due to the strong backscattering effect by their coccoliths (detached or attached), they influence the optical characteristics of the environment in two aspects: causing a high reflectance from the ocean surface; (and) making a large impact on the light field in upper ocean, by reducing the amount of available light beneath (Ackleson et al, 1988;Balch et al, 1989).…”

“…To monitor the development of coccolithophore blooms, regions of high occurrence were selected based on the following procedure: first, a global distribution of coccolithophores, mapped by Brown and Yoder (1994a) and Brown (1995) was considered; secondly, eight years of global distribution of PIC (from MODIS-Aqua) were monitored as monthly composites; and finally coccolithophore field studies were analyzed (Brown and Podesta, 1997;Balch et al, 1991;Holligan et al, 1993;Garcia et al, 2011;Raitsos et al, 2006;Painter et al, 2010;Burns, 1977;Tilburg et al, 2002). Based on these pre-investigations, three regions have been selected (Fig.…”

A Review of Ocean/Sea Subsurface Water Temperature Studies from Remote Sensing and Non-Remote Sensing Methods

“…This variation can also be applied to estimate absolute variations in the surface layer depth [81,82]. The correlation between SSH and thermocline depth is decreased by dipper and more diffuse thermocline and powerful surface buoyancy fluxes.…”