Estimating underwater light regime under spatially heterogeneous sea ice in the Arctic

Abstract: The vertical diffuse attenuation coefficient for downward plane irradiance (Kd ) is an apparent optical property commonly used in primary production models to propagate incident solar radiation in the water column. In open water, estimating Kd is relatively straightforward when a vertical profile of measurements of downward irradiance, Ed, is available. In the Arctic, the ice pack is characterized by a complex mosaic composed of sea ice with snow, ridges, melt ponds, and leads. Due to the resulting spatially heterogeneous light field in the top meters of the water column, it is difficult to measure at single-point locations meaningful Kd values that allow predicting average irradiance at any depth. The main objective of this work is to propose a new method to estimate average irradiance over large spatially heterogeneous area as it would be seen by drifting phytoplankton. Using both in situ data and 3D Monte Carlo numerical simulations of radiative transfer, we show that (1) the large-area average vertical profile of downward irradiance, Ed(z), under heterogeneous sea ice cover can be represented by a single-term exponential function and (2) the vertical attenuation coefficient for upward radiance (KLu), which is up to two times less influenced by a heterogeneous incident light field than Kd in the vicinity of a melt pond, can be used as a proxy to estimate Ed(z) in the water column

A multimodal endoscopic approach for characterizing sea-ice optics, physics, biology and biogeochemistry at small scale

Sea ice is a complex and heterogeneous medium that hosts a rich community of microbial organisms and small invertebrates. This ecosystem is shaped by a network of inhabitable spaces where the upward and downward fluxes of solutes and light support primary production, and ultimately the whole sea-ice trophic network. Describing the optical, physical, biological and biogeochemical processes that drive the functioning of the sea-ice ecosystem at the appropriate, i.e. small scale (micro- to centimeter), is very challenging. This medium is solid, fragile and highly heterogeneous. Traditional sea-ice sampling methods based on coring are most often coarse and destructive. Not only do they not allow the small scale to be explored, they generally alter the material to be analyzed. Here, we present a new approach for measuring relevant variables of the sea-ice ecosystem at small scale and, as much as possible, non-destructively. Inspired by medical endoscopes, the custom-built platform is intended to carry various types of miniaturized optical sensors for radiometry, chemistry and high-resolution imaging of the sea-ice interior. In this presentation, we will describe the concept and present the progress made to date

Green Edge ice camp campaigns : understanding the processes controlling the under-ice Arctic phytoplankton spring bloom

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797∘ N, 63.7895∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies

Satlantic’ SeaWiFS Profiling Multichannel Radiometer (SPMR s/n006) and Multichannel Surface reference (SMSR s/n 006). Calibration history report (2001-2011)

Validation of the “geophysical products” derived from observations of satellite ocean colour sensors requires the collection of the same parameters from in situ instrumentation. In particular, the irradiance reflectance or the remote sensing reflectance have to be determined from field measurements of radiometric quantities such as the upward and downward plane irradiances at various depths in the water column. This task has been performed in the frame of the BOUée pour l’acquiSition d’une Série à Long termE (BOUSSOLE) project by using a commercial radiometer system specifically designed for that purpose. This system is built by the Satlantic company (Halifax, Nova Scotia, Canada). It is composed on an in-water profiling radiometer called the “SeaWiFS Profiling Multichannel Radiometer” (SPMR) and a deck reference called the “SeaWiFS Multichannel Surface reference” (SMSR). Deployment procedures and data processing are succinctly presented hereafter. The Satlantic’ SPMR was specifically designed to collect data for validation of the National Aeronautics and Space Administration (NASA) Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color instrument. The SPMR/SMSR system that was built for the remote sensing group of the Laboratoire d’Océanographie de Villefranche (LOV) measures both downward and upward underwater irradiance in 13 spectral channels (Ed(λ) and Eu(λ), respectively), and the above-water downward irradiance in the same 13 channels (Es(λ)). These 13 channels were adapted to the band set of the European Space Agency (ESA) Medium Resolution Imaging Spectrometer (MERIS). The LOV SPMR/SMSR is serial number 006. This system was bought in 1994 and has been used since then, until it was lost at sea during BOUSSOLE cruise 110 in April 2011. It was deployed during a number of oceanographic cruises before being used for BOUSSOLE, and still on a few occasion during the course of the project, from 1996 to 2009 (MINOS in 1996 in the Mediterranean, COASTLOOC in 1996-1997 in European coastal waters, PROSOPE in 1999 in the Mediterranean, POMME in 2000 in the Northeastern Atlantic, BIOSOPE in 2004 in the Southeast Pacific, BATS in 2009 in the Bermuda area, and Plumes & Blooms in 2009 in the Santa Barbara channel). From July 2001 to April 2011, the SPMR/SMSR 006 was essentially used during the monthly BOUSSOLE cruises, during which more than 800 profiles were collected. This report summarizes the calibration history of these instruments. It does not include the description of the data processing that allows derivation of apparent optical properties from the profiles of radiometric quantities

Hydrographic (CTD) profiles in the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

During Leg 1, the CTD (CTD RBR Maestro) was manually lowered in the water through an ice hole with a velocity of less than 0.3 ms-1 and an acquisition frequency of 6 Hz, yielding a vertical resolution of a few centimetres. During legs 2 to 4, the CTD (CTD RBR Concerto) was installed on a Seabird Scientific optical package frame, which was deployed with a velocity of 0.3 m s-1 and an acquisition frequency of 8 Hz. Only data from downcasts were used and poor quality profiles, that had been affected by ice-covered sensors, were removed. Atmospheric pressure observed at weather stations near the sampling locations (Aklavik, Inuvik, Shingle Point and Tuktoyaktuk) was used to tare the CTD pressure sensors. CTD profiles were smoothed and binned to a regular 0.01 m depth grid

Temperature and salinity in the surface water of the Mackenzie Delta Region during 4 expeditions from spring to fall in 2019

During Leg 1, the CTD (CTD RBR Maestro) was manually lowered in the water through an ice hole. During legs 2 to 4, the CTD (CTD RBR Concerto) was installed on a Seabird Scientific optical package frame. Poor quality profiles, that had been affected by ice-covered sensors, were removed. Atmospheric pressure observed at weather stations near the sampling locations (Aklavik, Inuvik, Shingle Point and Tuktoyaktuk) was used to tare the CTD pressure sensors. The salinity was re-measured on discrete water samples (Sal Lab) using Mettler Toledo Conductivity/Salinity/pH meter

Seasonal and interannual variability of ocean color and composition of phytoplankton communities in the North Atlantic, Equatorial Pacific and South Pacific

International audienceMonthly averaged level-3 SeaWiFS chlorophyll concentration data from 1998 to 2001 are globally analyzed using Fourier's analysis to determine the main patterns of temporal variability in all parts of the world ocean. In most regions, seasonal variability dominates over interannual variability, and the timing of the yearly bloom can generally be explained by the local cycle of solar energy. The studied period was influenced by the late consequences of the very strong El Niño of 1997-98. After this major event, the recovery to normal conditions followed different patterns at different locations. Right at the equator, chlorophyll concentration was abnormally high in 1998, and then decreased, while aside from the equator, it was low in 1998, and increased later when equatorial upwelled waters spread poleward. This resulted in opposed linear trends with time in these two zones. Other noticeable examples of interannual variability in the open ocean are blooms of Trichodesmium that develop episodically in austral summer in the south-western tropical Pacific, or abnormally high chlorophyll concentration at 5°S in the Indian Ocean after a strong Madden-Julian oscillation. Field data collected quarterly from November 1999 to August 2001, owing to surface sampling from a ship of opportunity, are presented to document the succession of phytoplankton populations that underlie the seasonal cycles of chlorophyll abundance. Indeed, the composition of the phytoplankton conditions the efficiency of the biological carbon pump in the various oceanic provinces. We focus on the north Atlantic, Caribbean Sea, Gulf of Panama, equatorial Pacific, south Pacific subtropical gyre, and south-western tropical Pacific where these field data have been collected,. These data are quantitative inventories of pigments (measured by HPLC and spectrofluorometry), and picoplankton abundance (Prochlorococcus, Synechococcus, Picoeucaryotes and bacteria). There is a contrast between temperate waters where nanoplankton (as revealed by pigments indexes) dominate during all the year, and tropical waters where picoplankton dominate. The larger microplankton, that make most of the world ocean export production to depth, rarely exceed 20% of the pigment biomass in the offshore waters sampled by these cruises. Most of the time, there are large differences in the phytoplankton composition between cruises made at the same season on two different years