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Methodology:
\nA marine snow imaging system was lowered through the water column to acquire photographs of aggregates but these images also included abandoned (ghost) Phaeocystis colonies that are enumerated in this data set. The imaging system consisted of a collimated strobe system and either a 35-mm film camera (Lobsiger Deepslope 6000; Years 1 - 3) or a digital camera (Insite Pacific Scorpio; Year 4) mounted on an aluminum frame. The system was lowered at a rate of 10 m min-1 through the water column, acquiring ca. six images min-1 at an interval of ca. 1.7 m throughout the entire water column. Illumination was provided by a pair of strobe lights (Deep Sea Power and Light) positioned to produce an 8.4-cm deep beam of uniform, collimated light 66 or 79 cm from the camera lens. Aggregates larger than 0.5 mm within this volume (3 - 15 L, depending on the camera, lens and resultant geometry) are quantified from images taken by a camera that is mounted perpendicular to the long axis of the light beam, which can subsequently be distinguished and quantified by digital analysis. Ambient light illuminates particles in front of and behind this light beam and invalidates the calculation of illuminated volume. Thus, profiles were obtained near local midnight whenever possible (24-h photoperiods occurred throughout all cruises) to minimize this interference; images with the frame visible, due to ambient light, were discarded. The depth of first aggregate counts ranged from 30 - 88 m (a function of water clarity and solar angle). A Sea-Bird SeaCat CTD and 25-cm SeaTech transmissometer mounted on the camera frame provided continuous measurements of temperature, salinity and optical transmission. These data were used to calculate the depth at which each image was acquired. All film (Tmax 400) and images were returned to the laboratory for processing except for short sections viewed at sea to assess camera operation. The films were developed and then digitized to JPG format either in house, using a Nikon camera and macro lens (3767 x 2368), or commercially (3544 x 2341).
Abundance and size distribution of abandoned (ghost) Phaeocystis colonies from profiles conducted during R/V Polar Star cruises in the Ross Sea, Antarctica between 2001 and 2005.
\nRelated dataset (collected during the same profiles):
IVARS Marine Snow Profiles: https://www.bco-dmo.org/dataset/719478
The images were analyzed with Image Pro Plus, with a final resolution of the digitized images (2048 x 1536 pixels) of 4.2 pixels mm-1. Digital images were analyzed directly with a final resolution of 4.2 Pixels mm-1. To insure that the same portion of each image was analyzed, an area of Interest (AOI) was created within the region of maximum illumination. This AOI was positioned to the same location within each image before particles were counted. Within this AOI, Phaeocystis were identified by the analyst and counted separately from the much more abundant marine snow aggregates.\u200b
\nBCO-DMO Data Manager Processing Notes:
\n* station information added to marine snow data from separate Excel spreadsheet.
\n* various date formats in the date column changed to ISO 8601 (yyyy-mm-dd)
\n* longitude was decimal degrees with directional (W E), corrected so longitude negative for W, positive for E.
\n* replaced comma in station comment with ; to better support export as csv format
\n* removed padded whitespaces
\nFrom originally submitted profiles in individual Excel sheets:
\n* copied and pasted contests of sheets (contained data by profile) into two separate tables to concatenate all the profiles together. Split into two "datasets" for marine snow and Phaeocystis ghost colonies.
\n* Some sheets in the original file had two separate tables in each of the sheets (for profiles that didn't have canister letter). Separate datasets made for particles per liter and ghost colonies.
\n* Changed column names so they could be imported into BCO-DMO data system (column names can't start with number or contain > or - characters. e.g. column named "0.0 - 0.5" changed to "bin_0_0_to_0_5" and "> 2.5 - 3.0" changed to "bin_gt_2_5_to_3_0"
version 2 (2019-06-12) replaces version 1 (2019-05-28):
\n* The latitude and longitude maximum and minimum bounds updated. The latitude changed to negative values. The latitude and longitude in the dataset itself remain unchanged as they were accurate.