Hurricane Arthur and its effect on the short-term variability of &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; on the Scotian Shelf, NW Atlantic

Jonathan Lemay,Katja Fennel,Susanne E Craig,Blair J W Greenan,Helmuth Thomas,William J Burt

doi:10.5194/bg-15-2111-2018

Abstract

Abstract. The understanding of the seasonal variability of carbon cycling on the Scotian Shelf in the NW Atlantic Ocean has improved in recent years; however, very little information is available regarding its short-term variability. In order to shed light on this aspect of carbon cycling on the Scotian Shelf we investigate the effects of Hurricane Arthur, which passed the region on 5 July 2014. The hurricane caused a substantial decline in the surface water partial pressure of CO2 (pCO2), even though the Scotian Shelf possesses CO2-rich deep waters. High-temporal-resolution data of moored autonomous instruments demonstrate that there is a distinct layer of relatively cold water with low dissolved inorganic carbon (DIC) slightly above the thermocline, presumably due to a sustained population of phytoplankton. Strong storm-related wind mixing caused this cold intermediate layer with high phytoplankton biomass to be entrained into the surface mixed layer. At the surface, phytoplankton begin to grow more rapidly due to increased light. The combination of growth and the mixing of low DIC water led to a short-term reduction in the partial pressure of CO2 until wind speeds relaxed and allowed for the restratification of the upper water column. These hurricane-related processes caused a (net) CO2 uptake by the Scotian Shelf region that is comparable to the spring bloom, thus exerting a major impact on the annual CO2 flux budget.

Highlights

Coastal oceans constitute the interface of four compartments of the Earth system: land, ocean, sediment, and atmosphere
The data used in the present paper reflect the reoccurring winter storm pattern, with a periodicity of approximately 6 days as reported earlier for the region (Smith et al, 1978; Shadwick et al, 2010; Thomas et al, 2012)
Wind speeds for 2014 (Fig. 5b) show that during the winter, winds are stronger on the Scotian Shelf, with higher storm frequency, while wind speeds are generally lower during the spring and summer months

Summary

Introduction

Coastal oceans constitute the interface of four compartments of the Earth system: land, ocean, sediment, and atmosphere. Coastal oceans receive runoff from land (Chen and Borges, 2009) and are impacted by the open oceans. They are a hot spot for biological production, accounting for a disproportionate amount of global ocean production relative to their surface area (Cai et al, 2003; Borges et al, 2005). Coastal seas account for one-fifth to one-third of ocean primary production even though they only account for 8 % of the ocean surface area (Walsh, 1991). Due to their dynamic nature, coastal oceans experience much higher spatial and temporal variability (diel, seasonal, and annual) than the open oceans

Methods

Results

Conclusion