Exploring Ocean Biogeochemistry Using a Lab-on-Chip Phosphate Analyser on an Underwater Glider

Abstract

The ability to make measurements of phosphate (PO43–) concentrations at temporal and spatial scales beyond those offered by shipboard observations offers new opportunities for investigations of the marine phosphorus cycle. We here report the first in situ PO43– dataset from an underwater glider (Kongsberg Seaglider) equipped with a PO43– Lab-on-Chip (LoC) analyser. Over 44 days, a 120 km transect was conducted in the northern North Sea during late summer (August and September). Surface depletion of PO43– (<0.2 μM) was observed above a seasonal thermocline, with elevated, but variable concentrations within the bottom layer (0.30–0.65 μM). Part of the variability in the bottom layer is attributed to the regional circulation and across shelf exchange, with the highest PO43– concentrations being associated with elevated salinities in northernmost regions, consistent with nutrient rich North Atlantic water intruding onto the shelf. Our study represents a significant step forward in autonomous underwater vehicle sensor capabilities and presents new capability to extend research into the marine phosphorous cycle and, when combined with other recent LoC developments, nutrient stoichiometry.

Lab-on-Chip for In Situ Analysis of Nutrients in the Deep Sea

“…A sleep mode allows the electronics package to enter a lowpower mode between measurements, drawing <0. 25 When operating continuously, the average power consumption (dominated by the pump and valves) is 1.8 W. Nitrate Sensor Variant. Typical operation of the LOC nitrate system consists of the measurement of a blank solution, followed by the sample solution (e.g., ambient seawater) and an onboard standard solution.…”

“…Previous work has reported lab-on-chip nutrient analysis systems performing in situ measurements in a range of aquatic surface environments (estuaries, , rivers and glacial meltwater) as well as shallow ocean deployments. , Recently, lab-on-chip nitrate analyzers have been deployed on Kongsberg Seagliders in shallow shelf seas. , Here, we present the first demonstration of LOC platforms for in situ nitrate and phosphate analysis in the deep sea. We present the first deep (>200 m) in situ ocean nutrient profiles conducted using a LOC analyzer.…”

“…22,23 Recently, lab-on-chip nitrate analyzers have been deployed on Kongsberg Seagliders in shallow shelf seas. 24,25 Here, we present the first demonstration of LOC platforms for in situ nitrate and phosphate analysis in the deep sea. We present the first deep (>200 m) in situ ocean nutrient profiles conducted using a LOC analyzer.…”

Industry Partnership: Lab on Chip Chemical Sensor Technology for Ocean Observing

“…The combination of sensor and glider enabled accurate data at high resolution, on both spatial and temporal scales. A phosphate sensor has been integrated with a Seaglider as part of the AlterEco project (NE/P013899/1, NERC, United Kingdom) completing a 120 km transect in North Sea in 44 days observing reduction in surface concentrations and variations in the bottom mixed layer (Birchill et al, 2021). A pH sensor was also integrated into a Seaglider (iRobot/Kongsberg, part of the UEA fleet, United Kingdom) and used in the North Sea for 10 days together with O 2 and salinity data to derive CO 2 content air sea fluxes of oxygen and CO 2 demonstrating high spatial and temporal resolution (Possenti et al, 2021).…”

Ion chromatograph with three‐dimensional printed absorbance detector for indirect ultraviolet absorbance detection of phosphate in effluent and natural waters

“…The LOC in-situ phosphate analyzer developed by the National Oceanography Centre, Southampton can be seen as a leading phosphate analyzer. This portable analyzer has successfully been deployed within a broad range of environmental waters over long deployment periods delivering high levels of accuracy and precision [26][27][28]. Despite these high levels of analytical performance in the field, challenges arise in terms of mass manufacture of microfluidic components and assembly of LOC systems which have hampered these in-situ systems and other LOC colorimetric based systems from routine use and adoption on a mass scale [29,30].…”