Summer Ekman Pumping and its Implications to the Deep Water Renewal in Massachusetts and Cape Cod Bays

The area of Massachusetts and Cape Cod Bays (MB) is a semi-enclosed embayment surrounded by the Greater Boston Metropolitan Area, Cape Cod and the coastal communities from Boston to Cape Ann. An understanding of physical and biological processes in MB is critical to the local fishing industry, recreation and nature conservation. Our studies focus on wind driven currents, Ekman pumping induced coastal jets and water renewal in the deep basin of MB using both field observations and modeling. Results indicate that the characteristics of the deep water in Stellwagen Basin, the only deep basin in MB, are similar to the Gulf of Maine (GOM) water during early summer; and are significantly different from the GOM water during late summer. This suggests that the deep water exchange between MB and the GOM is limited during summer. The modeled results reveal that the Ekman pumping during a wind event induces coastal upwelling or downwelling, and produces fronts and coastal jets in response to baroclinic pressure gradients and surface slopes. The surface Ekman transport enhances the deep water renewal by pumping deep water from the GOM to Stellwagen Basin through the North Passage off Cape Ann, and by crossing over the shallow Stellwagen Bank. The time scales to spin up geostrophic currents during wind events and to renew the deep basin water in MB are also estimated.