THE OCEAN PLANET

The ocean planet

The ocean planet

Introduction

The presence of continental ice sheets and permafrost played a profound role in subsurface hydrology of glaciated regions over the last approximately 2 Myr . As these kilometer-thick ice sheets advanced and retreated across sedimentary basins, recharge was likely enhanced from the infiltration of subglacial meltwaters. During periods of permafrost development, and/or frozen ice cover, recharge was likely blocked or limited. As anomalous fluid pressures (e.g. remnant over- or under-pressure zones) from continental glaciation can be difficult to distinguish from other natural processes, such as erosion and sedimentation, their existence is somewhat speculative. Solute and isotope tracers in glaciated groundwater systems provide important constraints on the timing and source of recharge.

Specifically, basinal brines typically have much higher Ca concentrations than evaporated modern seawater, with Ca molalities, mCa > ?[mSO4 + ½mHCO3 + mCO3], implying some Ca balanced by Cl.

In this study, we review geochemical and isotopic evidence for groundwaters, which were recharged during the Pleistocene or early Holocene, from recent field studies of sedimentary aquifer systems throughout North America, Europe, Greenland, and Antarctica. To do so, we outline common tracers used to identify paleo groundwaters, identify the chemical and isotopic compositions of endmember source waters, and then summarize the key findings from hydrogeologic studies of sedimentary basins containing Pleistocene waters.

By combining these case studies, we provide a continental-scale perspective of how glaciation, permafrost, and sea-level lowstands altered groundwater circulation in sedimentary aquifers. We conclude with a synthesis of major findings and recommendations for future research to further understanding of ice sheet-permafrost-sediment interactions.

Constraining the mechanisms, penetration depths, and sources of recharge to sedimentary basins is important for understanding basinal-scale hydrodynamics, impacts of climate change on groundwater systems, and extent of freshwater resources on the continents and in coastal aquifers. In addition, these results have important implications for long-term safe and effective storage of anthropogenic waste products (e.g. radionuclides and carbon dioxide) in sedimentary basins at northern latitudes, which may be impacted by future glaciations.

Buried carboxylic groups from the side chains of aspartic (Asp) and glutamic (Glu) acids are often found in the active sites of proteins. Despite the low pK^sub a^ values (typically ~4) of exposed carboxylic groups, many buried carboxylic groups exhibit anomalously shifted-pK^sub a^ values (Creighton, 1997), some as high as 11 (Meyer et al., 2003; Szaraz et al., 1994). Due to large increases in pK^sub a^ values, these ionizable groups are protonated at neutral pH conditions. The pK^sub a^ values of these groups may change dramatically during the functional processes of proteins, resulting in deprotonation and proton transfer (Song et al., 2003; Xie et al., 2001). Hydrogen-bonding interactions play key roles in regulating the pK^sub a^ values of ionizable groups and in driving proton transfers.

Any scenario for basinal brine genesis is complicated by the fact that studies of fluid inclusions in Phanerozoic marine halites have shown that significant variations in the relative concentrations of Mg, Ca, Na, and SO4 existed in ancient ...