Fracture zones in the Mid Atlantic Ridge lead to alterations in prokaryotic and viral parameters in deep-water masses.

Simone Muck,Nicole Köstner,Gerhard J Herndl,Christian Winter,Thomas Griessler,Adam Klimiuk

doi:10.3389/fmicb.2014.00264

Simone Muck, Nicole Köstner + Show 4 more

Open Access

https://doi.org/10.3389/fmicb.2014.00264

Copy DOI

Abstract

We hypothesized that mixing zones of deep-water masses act as ecotones leading to alterations in microbial diversity and activity due to changes in the biogeochemical characteristics of these boundary systems. We determined the changes in prokaryotic and viral abundance and production in the Vema Fracture Zone (VFZ) of the subtropical North Atlantic Ocean, where North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) are funneled through this narrow canyon and therefore, are subjected to intense vertical mixing. Consequently, salinity, potential temperature, oxygen, PO4, SiO4, NO3 were altered in the NADW inside the VFZ as compared to the NADW outside of the VFZ. Also, viral abundance, lytic viral production (VP) and the virus-to-prokaryote ratio (VPR) were elevated in the NADW in the VFZ as compared to the NADW outside the VFZ. In contrast to lytic VP, lysogenic VP and both the frequency of lytically (FIC) and lysogenically infected cells (FLC) did not significantly differ between in- and outside the VFZ. Generally, FIC was higher than FLC throughout the water column. Prokaryotic (determined by T-RFLP) and viral (determined by RAPD-PCR) community composition was depth-stratified inside and outside the VFZ. The viral community was more modified both with depth and over distance inside the VFZ as compared to the northern section and to the prokaryotic communities. However, no clusters of prokaryotic and viral communities characteristic for the VFZ were identified. Based on our observations, we conclude that turbulent mixing of the deep water masses impacts not only the physico-chemical parameters of the mixing zone but also the interaction between viruses and prokaryotes due to a stimulation of the overall activity. However, only minor effects of deep water mixing were observed on the community composition of the dominant prokaryotes and viruses.

Highlights

In the marine environment, frontal systems are generally considered hotspots of diversity and activity (Doney et al, 2004; Longhurst, 2007; Ribalet et al, 2010), show typical characteristics of ecotones
The potential temperature of the Antarctic Bottom Water (AABW), the Antarctic Intermediate Water (AAIW) and the Lower North Atlantic Deep Water (LNADW) was significantly lower in the Vema Fracture Zone (VFZ) than outside the VFZ
In the VFZ, PO4, NO3, and SiO4 concentrations were significantly higher in the AABW and significantly lower in the Upper North Atlantic Deep Water (UNADW) than in the corresponding water masses outside the VFZ

Summary

Introduction

Frontal systems (vertical boundary systems of water masses) are generally considered hotspots of diversity and activity (Doney et al, 2004; Longhurst, 2007; Ribalet et al, 2010), show typical characteristics of ecotones. In the deep ocean, mixing of water masses is pronounced in areas where different water masses are funneled through canyons such as in the fracture zones of the Mid Atlantic Ridge These fracture zones represent major conduits of deep waters between the eastern and the western basin of the Atlantic and represent ideal sites to study the effect of mixing of deep-water masses on microbial and viral activity and diversity. Water masses funneled through fracture zones are potentially subjected to nutrient and material input from the slopes and bottom due to resuspension of sediments (Sloth et al, 1996) These fracture zones might be sites of larger changes in the microbial and viral community in specific water masses than in the same water mass outside the fracture zones. We focused on the Vema Fracture Zone (VFZ) of the MidAtlantic Ridge (Demidov et al, 2007), a well-studied region with intense mixing of well-defined deep-water masses and topography (Eittreim et al, 1983; Fischer et al, 1996), to study the interaction and changes in parameters describing viral and prokaryotic communities

Methods

Results

Discussion

Conclusion