Optical impact of an Emiliania huxleyi bloom in the frontal region of the Barents Sea

Abstract

The impact on downwelling irradiance of phytoplankton, cromophoric dissolved organic matter (CDOM) and particulate inorganic carbon (PIC) in the form of coccoliths, is described using a radiative transfer model and field data from the Barents Sea (BS). While annual Emiliania huxleyi blooms in the BS have been detected with satellite remote sensing, this is the first bio-optical field study on E. huxleyi from this area. Bio-optical variables were measured in August 2007 along a transect through the Polar Front from Arctic Water (ArW) into an E. huxleyi bloom in Atlantic Water (AW). The depth of the euphotic zone was on average 52 m in ArW, 45 m in frontal mixed water (FMW) and 21 m in AW. At the 10% irradiance depth in AW, phytoplankton had attenuated 40%, CDOM 17% and PIC 18% of the irradiance from 400 to 700 nm. Numbers from ArW were 36%, 26% and b 1%, respectively. The relative potential for Primary Production (PP pot ) in AW was 1.8× higher than in ArW, and PIC had reduced PP pot in AW by 20-40% at stations with ~100-130 mg PIC m −3 . A novel approach for estimating PIC based on a theoretical relationship between diffuse attenuation and irradiance reflectance is also described.

Dynamics regulating major trends in Barents Sea temperatures and subsequent effect on remotely sensed particulate inorganic carbon

“…Counts of Emiliania huxleyi cells from water samples were performed at the Flødevigen marine station by the Institute of Marine Research (IMR, Bergen) in 2005, and the Norwegian Component of the Ecosystem Studies of Subarctic and Arctic Regions (NESSAR) project in 2007, by means of light microscopy as described in Hovland et al (2013). Satellite-derived PIC values were extracted from the weekly scene that contained data closest in time and location to the corresponding cell count, whereupon the bloom threshold of PIC was calculated by linear regression forced through the origin.…”

“…Satellite images from the Barents Sea are often affected by cloud cover (Hovland et al 2013), and this was the case especially for the northern part of the ROI. To account for this, and to avoid the error that would result from variable coverage from week to week, we used a 'composite' procedure where missing data pixels in a scene were filled in with the value from the week before.…”

“…Since PIC is loga rithmically distributed, geometric mean was em ployed for these calculations. The weekly standing stocks of PIC were calculated assuming a uniform vertical distribution from the surface to 15 m depth (Hovland et al 2013).…”

“…The coccolithophorid Emiliania huxleyi (Lohmann) appears to have advanced into the sub-Arctic Bering and Barents Seas during the last 3 decades and has established annual bloom events in both areas (Merico et al 2003, Smyth et al 2004, Suk hanova et al 2004, Hovland et al 2013. En han ced stratification, low nutrient availability and relatively high irradiance are considered important inducing conditions for E. huxleyi blooms (Nanninga & Tyrrell 1996, IglesiasRodríguez et al 2002.…”

“…In the bloom phase of Emiliania huxleyi, PIC concentrations may not correlate with chlorophyll a (chl a), so using PIC as a proxy for E. huxleyi biomass should be done with caution (Van Bleijswijk et al 1994, Volent et al 2011, Hovland et al 2013). Therefore, the expression 'bloom' in this paper is used as a biogeochemical term referring to bulk PIC from coccoliths rather than phytoplankton biomass.…”