Zooplankton distribution patterns and vertical patchiness as they vary between stratified to deeply mixed ocean conditions.

Yoav Lindemann1, Jules S Jaffe2, Paul L Roberts3 and Amatzia Genin1, (1)The Hebrew University of Jerusalem, The Inter-university Institute for Marine Sciences, Eilat, Israel, (2)Scripps Institution of Oceanography, La Jolla, CA, United States, (3)Scripps Institution of Oceanography, UC San Diego, La Jolla, CA, United States
Zooplankton drifting in the open ocean are key drivers of ecological and biogeochemical processes.
A weighty portion of zooplanktonic biomass depends on ocean currents and water-column density gradients to determine the spatial distribution patterns of planktonic individuals. In this study we use ZOOPS, the Zooplankton Sonar, to measure the vertical distribution and the small scale interaction between zooplanktonic individuals, measured in the order of <1 cm across a series of >300 m deep vertical profiles. Three series of cruises were conducted during the winters and springs of 2014, 2015-16, and 2017, yielding ~ 40 vertical ZOOPS profiles that mapped the distribution of particles and zooplankton across the water column in Eilat, Gulf of Aqaba, Northern Red Sea.
Water column physical conditions throughout the sampling periods varied between stable - stratified conditions, to deeply mixed conditions, reaching seasonal Mixed Layer Depth of >450 m depth.
Acoustic data were processed to measure the seasonal change in vertical zooplankton patchiness. The distribution patterns of single animals across each acoustic sample were measured, and the minimal distances between each pair of animals calculated. The expected frequency of minimal distances was modelled, and compared to measured in-situ distribution patterns.

In this study we seek measure the influence of physical ocean-surface processes (i.e. Mixed Layer Depth deepening due to surface cooling) on the distribution patterns of single animals hundreds of meters below the surface. The results and the implications of this study will be discussed.