The imbalance of new and export production in the western Antarctic Peninsula, a potentially “leaky” ecosystem

Abstract

AbstractTo quantify the balance between new production and vertical nitrogen export of sinking particles, we measured nitrate uptake, net nitrate drawdown, ΔO2/Ar‐based net community production, sediment trap flux, and 234Th export at a coastal site near Palmer Station, Antarctica, during the phytoplankton growing season from October 2012 to March 2013. We also measured nitrate uptake and 234Th export throughout the northern western Antarctic Peninsula (WAP) region on a cruise in January 2013. We used a nonsteady state 234Th equation with temporally varying upwelling rates and an irradiance‐based phytoplankton production model to correct our export and new production estimates in the complex coastal site near Palmer Station. Results unequivocally showed that nitrate uptake and net community production were significantly greater than the sinking particle export on region‐wide spatial scales and season‐long temporal scales. At our coastal site, new production (105 ± 17.4 mg N m−2 d−1, mean ± standard error) was 5.3 times greater than vertical nitrogen export (20.4 ± 2.4 mg N m−2 d−1). On the January cruise in the northern WAP, new production (47.9 ± 14.4 mg N m−2 d−1) was 2.4 times greater than export (19.9 ± 1.4 mg N m−2 d−1). Much of this imbalance can be attributed to diffusive losses of particulate nitrogen from the surface ocean due to diapycnal mixing, indicative of a “leaky” WAP ecosystem. If these diffusive losses are common in other systems where new production exceeds export, it may be necessary to revise current estimates of the ocean's biological pump.