Simulation of the global air‐sea transfer velocity field of helium

Abstract

Air‐sea exchange is important in constructing a budget of He in the upper oceanic water column. This exchange of He is controlled by the transfer velocity (KwHe) and the air‐sea concentration gradient. Here, the global transfer velocity field of He is computed for January and July with user‐defined derived fields based on control runs of the NCAR (National Center for Atmospheric Research) CCM1 (Community Climate Model), a 12 layer atmospheric general circulation model. The spatial resolution of these calculations is 4.5° × 7.5° latitude‐longitude. The range of KwHe variation over the globe is over an order of magnitude, varying from 5 to 75 cm hr−1. Equatorial values are generally 10‐20 cm hr−1 and high latitude regions experience values in excess of 60 cm hr−1. The annual variability of the transfer velocity in the high‐latitude northern hemisphere is larger than in the high‐latitude southern hemisphere. This work shows that the spatial and temporal variation in the global transfer velocity field of He is significant. This result should be included in future high‐resolution 3‐dimensional coupled ocean‐atmosphere tracer models when attempting to quantitatively deconvolute vertical transport and air‐sea exchange in surface ocean He budgets. This approach may allow high‐resolution global estimates of nitrate flux into the euphotic zone, an important component in oceanic biogeochemical modeling efforts.