Multi-century Hydroclimate Variability in the North Atlantic Basin during the Holocene and Potential Linkages to the Tropical Pacific

Abstract:

Circulation around the North Atlantic sub-tropical high shapes the hydro-climate of the North Atlantic basin with high precipitation rates common on the rising, western limb contrasting with low precipitation and descending air masses over the eastern sector. The extent, central location, and magnitude of the western precipitation plume shifts seasonally, but also responds to inter-annual variability including the remote effects of ENSO. Here, we compare those spatial patterns with Holocene hydro-climate changes to help diagnose dynamics on centennial to millennial scales. From 1948-2018, inter-annual winter precipitation variability on the coast exceeded that observed inland by >60%. El Nino years tended to increase winter precipitation over the western North Atlantic and, thus, increased the coastal-inland precipitation contrast in eastern North America. The winter precipitation difference between coastal areas, such as Cape Cod, Massachusetts, USA, and inland areas, such as Vermont, increased by 125-500 mm (100-400%) during El Nino years, and declined to near zero during La Nino years. Holocene precipitation reconstructions from the same regions, replicated by fossil pollen and lake-level changes from multiple sites in each area, likewise indicate that multi-century variability is greatest along the coast and that the inland-coastal precipitation difference has increased by 60 mm since 5.5 ka when El Nino-like precipitation patterns developed around the tropical Pacific. Wet phases in the coastal northeastern U.S. also increased the regional precipitation contrast by an additional 20 mm from 5.5-4.9, 4.6-4.3, 3.9-2.7, and 2.3-1.3 ka, and therefore, indicate that investigations into Pacific-Atlantic linkages on multi-centennial timescales during the Holocene are warranted.