a b s t r a c tSubmarine groundwater discharge (SGD) to the coastal environment along the eastern Yucatan Peninsula, Quintana Roo, Mexico was investigated using a combination of tracer mass balances and analytical solutions. Two distinct submarine groundwater sources including water from the unconfined surficial aquifer discharging at the beach face and water from a deeper aquifer discharging nearshore through submarine springs (ojos) were identified. The groundwater of nearshore ojos was saline and significantly enriched in short-lived radium isotopes ( 223 Ra, 224 Ra) relative to the unconfined aquifer beach face groundwater. We estimated SGD from ojos using 223 Ra and used a salinity mass balance to estimate the freshwater discharge at the beach face. Analytical calculations were also used to estimate wave set-up and tidally driven saline seepage into the surf zone and were compared to the salinity-based freshwater discharge estimates. ). Discharge at the beach face was in the range of 3.3-8.5 m 3 d À 1 m À 1 for freshwater and 2.7 m 3 d À 1 m À 1 for saline water based on the salinity mass balance and wave-and tidally-driven discharge, respectively. Although discharge from the ojos was larger in volume than discharge from the unconfined aquifer at the beach face, dissolved inorganic nitrogen (DIN) was significantly higher in beach groundwater; thus, discharge of this unconfined beach aquifer groundwater contributed significantly to total DIN loading to the coast. DIN fluxes were up to 9.9 mol d À 1 m À 1 from ojos and 2.1 mol d À 1 m À 1 from beach discharge and varied regionally along the 500 km coastline sampled. These results demonstrate the importance of considering the beach zone as a significant nutrient source to coastal waters for future management strategies regarding nutrient loading to reef environments and coastal development. This study also identifies the importance of understanding the connectivity of submarine spring discharge to the nearshore coastal environment and the impact of inland anthropogenic activities may have on coastal health.

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Submarine groundwater discharge (SGD) was quantified at select sites in San Francisco Bay (SFB) from radium ( 223 Ra and 224 Ra) and radon ( 222 Rn) activities measured in groundwater and surface water using simple mass balance box models. Based on these models, discharge rates in South and Central Bays were 0.3-7. − to NH 4 + available to phytoplankton with implications to bay productivity, phytoplankton species distribution, and nutrient uptake rates. This assessment of nutrient delivery via groundwater discharge in SFB may provide vital information for future bay ecological wellbeing and sensitivity to future environmental stressors.

Groundwater discharge has been recognized as an important process at the land-sea interface worldwide (Burnett et al. 2006; Moore 2010; and references therein). This process in coastal environments has been defined as SGD and includes all water, terrestrially derived freshwater and recirculated seawater crossing the sediment-water interface regardless of driving mechanism (Burnett et al. 2003; Michael et al. 2005; Taniguchi et al. 2006). Submarine groundwater can transport chemical constituents from land and seafloor sediments to coastal waters and therefore plays an important role in coastal geochemical budgets and ecosystem dynamics (e.g.,

The surface waters of the Southern Ocean play a key role in the global climate and carbon cycles by promoting growth of some of the world's largest phytoplankton blooms. Several studies have emphasized the importance of glacial and sediment inputs of Fe that fuel the primary production of the Fe-limited Southern Ocean. Although the fertile surface waters along the shelf of the western Antarctic Peninsula (WAP) are influenced by large inputs of freshwater, this freshwater may take multiple pathways (e.g. calving, streams, groundwater discharge) with different degrees of water-rock interactions leading to variable Fe flux to coastal waters. During the summers of 2012-13 and 2013-14, seawater samples were collected along the WAP, near Anvers Island, to observe water column dynamics in nearshore and offshore waters. Tracers ( 223,224 Ra, . These mixing rates suggest a rapid transport mechanism for moving meltwater offshore.