Solar and climate signals revealed by seasonal 10Be data from the NEEM ice core project for the neutron monitor period

Be-10 in ice cores has been instrumental for reconstructing past changes in solar activity prior to direct observations. For a robust use of these records, it is pivotal to understand the Be-10 transport and deposition. However, there are only few high-resolution seasonal Be-10 data longer than one full solar cycle (11 years) that could enable a quantification of the influences of atmospheric circulation and deposition processes on the Be-10 signal in ice. Here we present a seasonally resolved Be-10 data set covering the neutron monitor period (1951-2002) from a firn core connected to the NEEM (North Greenland Eemian Ice Drilling) project. The results suggest that both summer and winter Be-10 reflect the production signal induced by solar modulation of galactic cosmic rays. However, superimposed on this solar signal we find additional meteorologically driven influences on Be-10 transport and deposition. We found that the tropopause pressure over 30 degrees N represents an important factor influencing NEEM Be-10 concentrations on seasonal and annual scales. Be-10 deposited in summer also correlates significantly with the tropopause pressure over Greenland suggesting a direct contribution of stratospheric intrusions during summer to the Be-10 deposition in Greenland. To correct for these transport/deposition influences, we apply a first-order correction to the Be-10 data using a multi-linear regression model. The climate-corrected Be-10 data shows a comparable skill for reconstructing production rate changes as the Be-10 composite record from five different ice cores in Greenland. The results suggest that the correction approach can be a complementary method to the stacking to better isolate the production rate signal from the Be-10 data when only limited data are available. (C) 2020 Elsevier B.V. All rights reserved.