Estimates of potential new production (PNP) for the waters off the western Antarctic Peninsula (WAP) region

Abstract Potential new production (PNP) can be used as a proxy for new primary production (nPP) and sets the upper bound limit of nitrate-derived primary production (PP). For this study, we estimate PNP by employing a one-dimensional analytical model using in situ and model data for the waters off the western Antarctica Peninsula (WAP) for midsummer, centered around January. Field observations were made during the Palmer Long Term Ecological Research (Palmer LTER) program. A decade long time-series of NO 3 vertical profile data (1998–2007, N =516) was used for PNP computations. PNP was calculated for the WAP region by subdividing it into three sub-regions i.e. Coastal, Shelf and Slope based on bathymetry and water mass properties. The Coastal sub-region includes waters with bathymetric depths of 450 m or less with Slope water accounting for the oceanic region greater than 750 m water depth, while the extensive Shelf region occupies the area between these depth limits. Mean PNP estimates were computed to be 2482.6±197.5, 384.5±61.7, and 891.1±81.8 mg C m −2 d −1 for the Coastal, Shelf and Slope sub-regions, respectively. The estimated overall mean PNP rate for the entire Palmer LTER WAP region during midsummer (January) was 1257.5±113.6 mg C m −2 d −1 . The mean potential f -ratio (PNP:PP) for the WAP region was closer to unity (potential f -ratio=1.2) indicating that nPP (as opposed to recycled production) plays a major role in sustaining this sporadic but highly productive Antarctic ecosystem during mid-summer. We have also analyzed a longer time series from oceanic sampling stations off Palmer Station, Anvers Island, Antarctica spanning yeardays 310–45 (late November–mid February, 1994–2007). Harmonic regression fit of PNP data from all stations within this nearshore sampling grid of the Palmer LTER Program during the growth season provides maximum and minimum PNP rates of 2181.78 and 14.69 mg C m −2 d −1 on yeardays 335 (late November) and 43 (mid February), respectively. The overall mean PNP for this region was estimated to be 1040.93±764.58 mg C m −2 d −1 by employing a constant K z value of 10 −5 m s −2 . The maximum and minimum PNP values coincide approximately with the onset and demise of annual algal bloom. Analysis of the terms used in the PNP equation indicate that both NO 3 drawdown rates (mean=13.25±9.57 mmol m −2 d −1 , N =156) and NO 3 flux into the euphotic layer (mean=1.36±1.79 mmol m −2 d −1 , N =156) have high temporal and spatial variability. NO 3 drawdown rates were higher than NO 3 flux into the control volume by approximately an order of magnitude. Sensitivity analyses of the model using two extreme values of Kz, (10 −4 and 10 −5 m s −2 ) that are widely reported in the literature for the WAP region, yielded a PNP range of 97.13 mg C m −2 d −1 . The latter accounted for approximately 10% of the overall computed PNP. PNP estimates for the coastal sub-region which includes Marguerite Bay agreed well with estimates of nPP from north Marguerite Bay in a recent study which employed different datasets and research approach.