Toward High-Resolution Vertical Measurements of Dissolved Greenhouse Gases (Nitrous Oxide and Methane) and Nutrients in the Eastern South Pacific

Abstract

In this study, in situ, real-time and high-resolution vertical measurements of dissolved greenhouse gases (GHGs) such as nitrous oxide (N 2 O) and methane (CH 4 ) and nutrients are reported for the eastern South Pacific (ESP); a region with marked zonal gradients, ranging from highly productive and suboxic conditions in coastal upwelling systems to oligotrophic and oxygenated conditions in the subtropical gyre. Four high-resolution vertical profiles for gases (N 2 O and CH 4 ) and nutrients (NO − 3 and PO 3− 4 ) were measured using a Pumped Profiling System (PPS), connected with a liquid degassing membrane coupled with Cavity Ring-Down Spectroscopy (CRDS) and a nutrient auto-analyzer, respectively. The membrane-CRDS system maintains a linear response over a wide range of gas concentrations, detecting N 2 O and CH 4 levels as low as 0.0774 ± 0.0004 and 0.1011 ± 0.001 ppm, respectively. Continuous profiles for gases and nutrients were similar to those reported throughout the ESP, with pronounced N 2 O and CH 4 peaks at the upper oxycline and at the base of the euphotic zone and pycnocline, respectively, in the coastal zone; but almost constant depth profiles in the subtropical gyre. Additionally, other vertical gas and nutrient structures were observed using continuous sampling, which would not have been detected by discrete sampling. Our results demonstrate that continuous measurements can be a potentially useful methodology for future GHGs cycle studies.

Spatial Distribution of Dissolved Methane Over Extreme Oceanographic Gradients in the Subtropical Eastern South Pacific (17° to 37°S)

“…NO 3 − , NO 2 − , and PO 4 3− analysis were performed according to colorimetric techniques (Grasshoff et al., 1983) using a an AutoAnalyzer (SEAL Analytical AA3). However, during the CIMAR 21 cruise, given the extremely low (nanomolar) nutrient concentrations that were expected in the oligotrophic SESP region, the AutoAnalyzer was connected to a 500 mm Liquid Waveguide Capillary Cell (LWCC‐3050, World Precision Instrument), as recommended for submicromolar levels in NO 3 − and PO 4 3− (Troncoso et al., 2018). Chl‐a samples were analyzed using fluorometry (Turner Designs 10AUTM) according to standard procedures (Parsons et al., 1984).…”

“…In the coastal regions, upwelling brings cold and saline waters with high nutrient levels to the surface waters, which triggers nutrient fertilization, high chlorophyll‐a (Chl‐a) availability, as well as the presence of oxygen deficient waters (Naqvi et al., 2010; Thiel et al., 2007). In contrast, the subtropical gyre contains warm waters with significantly higher oxygen levels and undetectable nutrient and Chl‐a levels (Lepère et al., 2009; Ras et al., 2008; Troncoso et al., 2018). Given these conditions, it is likely that CH 4 levels will respond to gradients, as it is closely related with microalgal dynamics (Bogard et al., 2014; Leon‐Palmero et al., 2020), as well as with oxygen deficiency as a result of anaerobic methanogenesis, which in turn is fueled by organic matter (Reeburg, 2007).…”

A Harmonized Nitrous Oxide (N2O) Ocean Observation Network for the 21st Century

“…four CEAS systems and one FTIR system) for continuous dissolved N 2 O measurements was conducted in the Baltic Sea as part of the activities of SCOR WG 143, demonstrating good agreement between measurements obtained from the different systems. Only recently, a Pumped Profiling System (PPS), connected with a liquid degassing membrane coupled with CEAS has allowed real-time, high-resolution, vertically resolved measurements of sub-surface N 2 O (Troncoso et al, 2018). N2O-ON will encourage the wider use of these and emerging new technologies where they can contribute to improvements to data quality, measurement frequency and spatial resolution.…”

Isotopic Characterization of Water Masses in the Southeast Pacific Region: Paleoceanographic Implications

“…These results may be explained by the accumulation of respired 12 C during the passage of the ESSW along the highly productive upwelling systems off western South America and in situ intense redox processes in the coastal section (Chavez & Messié, 2009; Daneri et al., 2000; Montero et al., 2007; Vergara et al., 2017). Close to the coast methanogenesis within suspended particles has been observed in the pycno/oxyclines (Holmes et al., 2000; Naqvi et al., 2010; Sansone et al., 2001; Troncoso et al., 2018), resulting in the accumulation of methane depleted δ 13 C (Tenorio, 2021). This process may also be responsible for some of the highly depleted δ 13 C DIC values observed in ESSW.…”