Aerial infrared imaging reveals large nutrient‐rich groundwater inputs to the ocean

Abstract

[1] Regional high-resolution (0.1°C, 0.5 m) low-altitude thermal infrared imagery (TIR) reveals the exact input locations and fine-scale mixing structure of massive, cool groundwaters that discharge into the coastal zone as both diffuse flows and as >30 large point-sourced nutrient-rich plumes along the dry western half of the large volcanic island of Hawaii. These inputs are the sole source of new nutrient delivery to coastal waters in this oligotrophic setting. Water column profiling and nutrient sampling show that the plumes are cold, buoyant, nutrient-rich brackish mixtures of groundwater and seawater. By way of example, we illustrate in detail one of the larger plumes, which discharges ca. 12,000 m 3 d À1 (ca. 8,600 m 3 d À1 freshwater), rates comparable in volume to high-flux groundwater outputs in better-known tropical karst terrains. We further show how nutrient mixing trends may be integrated into TIR sea surface temperatures to produce surface water nutrient maps of regional extent.

Chemical weathering fluxes from volcanic islands and the importance of groundwater: The Hawaiian example

“…SGD fluxes from the Hawaiian Islands are poorly quantified, having been modeled in a few discrete locations only (Johnson et al, 2008;Knee et al, 2008;Street et al, 2008;Peterson et al, 2009), but none of these efforts have targeted the total SGD flux from an entire island or the archipelago as a whole. The USGS has performed whole-island water budget studies for all the major Hawaiian Islands except for the island of Hawai'i, where the water budget has been described in several regional studies (performed by the USGS, the State of Hawai'i and private companies), which together cover the entire island.…”

“…For example, SGD from the island of Hawai'i has a temperature of ~19-21°C (Johnson et al, 2008;Peterson et al, 2009), andConrad et al (1997) showed that groundwater in deep drill holes on the east flank of Kilauea volcano is the same temperature from sea level down to ~500 m below sea level -~20-25°C. The results from Rad et al (2007) are therefore not directly comparable with our work.…”

“…Several studies provide evidence that SGD is widespread in Hawai'i as well. Street et al (2008) used multiple chemical tracers (salinity, dissolved silica and Ra-isotopes) to quantify SGD in several locations in Hawai'i, Johnson et al (2008) used thermal infrared imagery to demonstrate the presence of large, cold freshwater plumes along the west coast of the island of Hawai'i and Peterson et al (2009) quantified the discharge via these plumes using salinity and Ra-isotopes. SGD is not only an important pathway for the delivery of water from land to ocean; it also transports significant amounts of dissolved solids from weathering on land directly to the global ocean (Rad et al, 2007;Georg et al, 2009).…”

Late Holocene14C Marine Reservoir Corrections for Hawai'I Derived from U-Series Dated Archaeological Coral

“…This value is insignificantly lower than our average value for Moloka'i of 52 ± 25 yr for AD 700-1800. However, the western Kona coast is known for large local groundwater discharge with 31 major point-source discharge plumes (surface area >13,000 m 2 ) along ~100 km of coastline (Johnson et al 2008). As the 14 C content in DIC of local groundwater may not be similar to that of surface ocean, the above coral ΔR value may be influenced by local groundwater discharge and is not used for the calculation of the weighted mean ΔR for Hawai'i, which is discussed later.…”

Linking regional sources and pathways for submarine groundwater discharge at a reef by electrical resistivity tomography, 222Rn, and salinity measurements

“…[3] Despite comprehensive efforts, one gap in SGD science that has been challenging to fill is a lack of observations which link offshore information from isotopic or chemical tracer measurements [Cable et al, 1996a;Moore, 1996], seepage measurements [Michael et al, 2003;Moore et al, 2002], ground-based [Moore et al, 2002] and remote thermal measurements [Johnson et al, 2008] to subsurface environments in offshore areas, coasts and further inland. However, there have been some recent comprehensive studies [Martin et al, 2007;Breier et al, 2009].…”