Acoustic Detection of Krill Scattering Layer in the Terra Nova Bay Polynya, Antarctica

et al. 2021

Front. Mar. Sci.

The Ross Sea, one of the most productive regions in the Southern Ocean, plays a significant role in deep water formation and carbon cycling. Dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) absorption and fluorescence (FDOM) properties were studied in conjunction with biophysical properties during austral summer. Elevated values of both DOC (mean 47.82 ± 5.70 μM) and CDOM (absorption coefficient at 325 nm, acdom325: mean 0.31 ± 0.18 m–1) observed in the upper shelf waters in the southwest (SW), north of the Ross Ice Shelf (RIS), the northwest and along a transect inward of the shelf break, suggested in situ production and accumulation linked to the productive spring/summer season. However, regional differences were observed in CDOM with acdom325 higher (0.63 ± 0.19 m–1) and its spectral slope S275–295 lower (24.06 ± 2.93 μm–1) in the SW compared to other regions (0.25 ± 0.08 m–1 and 28.92 ± 2.67 μm–1, respectively). Similarly, the specific UV absorption coefficient or SUVA254 determined at 254 nm was greater (1.85 ± 0.55 m2 mg–1 C) compared to other regions (1.07 ± 0.24 m2 mg–1 C), indicating CDOM of greater molecular weight and aromaticity in the SW. Phytoplankton absorption spectra indicated the shallow mixed layer of SW Ross Sea to be dominated by diatoms (e.g., Fragilariopsis spp.), a preferential food source for grazers such as the Antarctic krill, which in large numbers have been shown to enhance CDOM absorption, a likely source in the SW. Excitation-emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) retrieved one protein-like and two humic-like FDOM fractions commonly observed in the global ocean. In contrast to acdom325 which was uncorrelated to DOC, we observed weak but significant positive correlations between the humic-like FDOM with salinity and DOC, high value of the biological index parameter BIX and an instance of increasing FDOM with depth at a location with sinking organic matter, suggesting autochthonous production of FDOM. The absorption budget showed a relatively higher contribution by CDOM (70.7 ± 18.3%) compared to phytoplankton (22.5 ± 15.2%) absorption coefficients at 443 nm with implications to ocean color remote sensing. This first study of DOM optical properties provides additional insights on carbon cycling in the Ross Sea.

Section: Chromophoric Dissolved Organic Matter Sources In the Southwest Ross Seamentioning

confidence: 84%

Ross Sea Dissolved Organic Matter Optical Properties During an Austral Summer: Biophysical Influences

D’Sa

et al. 2021

Front. Mar. Sci.

“…Some organisms (C/SNSBF and LNSBF in this study) with densities similar to seawater have weak reflections (Stanton and Chu, 2000;Simmonds and MacLennan, 2005). Accordingly, different scatterers with different sizes, densities, and behavioral characteristics are expected to have different frequency responses among multiple frequencies (Kang et al, 2002(Kang et al, , 2016(Kang et al, , 2020. Frequency characteristics (involving frequency responses among multiple frequencies) are common means of classifying marine organisms.…”

Section: Considering the Mvbs Methods For Acoustic Categorizationmentioning

confidence: 99%

“…Additionally, it is nearly impossible to estimate accurate biomass values from acoustic data alone. Nevertheless, acoustic backscatter data from multiple frequencies can provide meaningful behavioral and ecological information (D'Elia et al, 2016;Kang et al, 2016Kang et al, , 2020Béhagle et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Sound Scattering Layers Within and Beyond the Seychelles-Chagos Thermocline Ridge in the Southwest Indian Ocean

Kang

et al. 2021

Front. Mar. Sci.

Self Cite

In global oceans, ubiquitous and persistent sound scattering layers (SL) are frequently detected with echosounders. The southwest Indian Ocean has a unique feature, a region of significant upwelling known as the Seychelles-Chagos Thermocline Ridge (SCTR), which affects sea surface temperature and marine ecosystems. Despite their importance, sound SL within and beyond the SCTR are poorly understood. This study aimed to compare the characteristics of the sound SL within and beyond the SCTR in connection with environmental properties, and dominant zooplankton. To this end, the region north of the 12°S latitude in the survey area was defined as SCTR, and the region south of 12°S was defined as non-SCTR. The results indicated contrasting oceanographic properties based on the depth layers between SCTR and non-SCTR regions. Distribution dynamics of the sound SL differed between the two regions. In particular, the diel vertical migration pattern, acoustic scattering values, metrics, and positional properties of acoustic scatterers showed two distinct features. In addition, the density of zooplankton sampled was higher in SCTR than in the non-SCTR region. This is the first study to present bioacoustic and hydrographic water properties within and beyond the SCTR in the southwest Indian Ocean.

“…To extract the E. pacifica echoes, this species identification was performed using the difference of the mean volume backscattering strength (∆MVBS) method, which is also known as the dB difference method [35][36][37][38]. The dB difference method depends on the frequency characteristics of the SSL attributable to marine organisms.…”

Section: Acoustic Data Analysis and E Pacifica Identificationmentioning

confidence: 99%

Spatial Distribution of Sound Scattering Layer and Density Estimation of Euphausia pacifica in the Center of the Yellow Sea Bottom Cold Water Determined by Hydroacoustic Surveying

Kım

et al. 2022

JMSE

The Yellow Sea Bottom Cold Water (YSBCW) refers to seawater with a water temperature of 10 °C or less found at the bottom of the center of the Yellow Sea. The spatiotemporal variability of the YSBCW directly affects the distribution of organisms in the marine ecosystem. In this study, hydroacoustic and net surveys were conducted in April (spring) to understand the spatial distribution of the sound scattering layer (SSL) and estimate the density of Euphausia pacifica (E. pacifica) in the YSBCW. Despite the shallow water in the YSBCW region, E. pacifica formed an SSL, which was distributed near the bottom during the daytime; it showed a diel vertical migration (DVM) pattern of movement toward the surface during the nighttime. The mean upward and downward swimming speeds around sunset and sunrise were approximately 0.6 and 0.3–0.4 m/min, respectively. The E. pacifica density was estimated in the central, western, and eastern regions; the results were approximately 15.8, 1.3, and 10.3 g/m2, respectively, indicating significant differences according to region. The results revealed high-density distributions in the central and eastern regions related to the water temperature structure, which differs regionally in the YSBCW area. Additional studies are needed regarding the spatial distribution of E. pacifica in the YSBCW and its relationship with various ocean environmental parameters according to season. The results of this study contribute to a greater understanding of the structure of the marine ecosystem in the YSBCW.