Assessment of Annual Physico-Chemical Variability via High-Temporal Resolution Monitoring in an Antarctic Shallow Coastal Site (Terra Nova Bay, Ross Sea)

Chiara Lombardi,Piotr Kuklinski,Edoardo Spirandelli,Andrea Bordone,Giancarlo Raiteri

doi:10.3390/min11040374

Abstract

The Southern Ocean is an important atmospheric carbon sink, and potential changes in the carbon flux in this region will affect the ocean as a whole. Thus, to monitor the variability of its physico-chemical parameters is becoming a priority. This study provides the first high-resolution all-year-round record of observed and computed physico-chemical data from a shallow coastal site in Terra Nova Bay (Ross Sea). From November 2018 to November 2019, an underwater observatory deployed at a 25 m depth under an ice pack recorded pressure (p), temperature (t), electrical conductivity (C), dissolved oxygen (DO), pH in total scale (pHT), and illuminance (Ev). Practical salinity (SP), density (ρ), tidal constituents, carbonate system parameters (total alkalinity (TA), carbon dioxide partial pressure (pCO2), calcite, and aragonite (ΩCa, ΩAr)), together with sea ice concentration (SIC) and chlorophyll-a (Chl-a), were derived from measured and satellite data. t, DO, and pHT displayed the lowest values between July and November (–1.95 °C, 6.61 mL L−1, 7.97) whereas the highest in January (+1.08 °C, 10.61 mL L−1, 8.35). SP had the lowest values (33.72 PSU) in February and the highest (34.87 PSU) in September. Ev peaked in March (201 lux), with the highest values (>50 lux) in correspondence to the lowest values of SIC and a delayed trend, between December and March, with respect to Chl-a values (0.2–1.1 mg m−3). ΩCa and ΩAr showed their highest average monthly values (±s.d.) in January (ΩCa: 3.41 ± 0.27; ΩAr: 2.14 ± 0.17), when DO had maximum values. The lowest Ω occurred in September (ΩCa: 2.11 ± 0.02; ΩAr: 1.32 ± 0.02), at the end of phytoplankton activity. No undersaturation for both calcite and aragonite was recorded during the study period. This study highlights that biological activities and physico-chemical variables of the investigated shallow coastal site are coupled and, in many cases, influence each other.

Highlights

We present and discuss the first high-resolution all-year-round record of observed and derived physical-chemical data set resulting from the Ross Sea
Mooring sites are well spread in Antarctica, recording physico-chemical seawater data in deep sites as well as describing Antarctic current dynamics [47,48,49] of sites, including
The data presented here are from the underwater observatory (Figure 2), anchored on the sea bottom at 25 m of depth under the ice pack, which allowed in situ seawater parameters to be recorded over 12 months (Figure 4, Table 2)

Summary

Introduction

Despite the continuous increase in atmospheric carbon dioxide (CO2 ) concentration, Antarctica and the Southern Ocean have experienced less uniform temperature changes and a general slowdown in the rate of warming across the past 30–50 years [3,4]. This might be due to a heat redistribution within the atmospherecryosphere system [5], with the reduction in atmospheric heating almost equating in terms of energy to the contemporaneous increases in ice melting. The effects of climate change on the continent and in the ocean are expected to exacerbate [6]

Methods

Results

Conclusion