Cm. Turley et Pj. Mackie, BACTERIAL AND CYANOBACTERIAL FLUX TO THE DEEP NE ATLANTIC ON SEDIMENTING PARTICLES, Deep-sea research. Part 1. Oceanographic research papers, 42(8), 1995, pp. 1453-1474
Long term (17 month) moored sediment trap studies during 1989/90 in th
e NE Atlantic reveal that heterotrophic bacteria and cyanobacteria are
transported into the deep-sea in large numbers (up to 32 x 10(9) cell
s/m(2)/day and 37 x 10(7) cells/m(2)/day, respectively) by attachment
to,or incorporation in, rapidly sedimenting particles. The fluxes of t
hese microorganisms follow the seasonal mass and POC flux patterns wit
h two major flux events at 3100 and 4465 m each year and another flux
event present only in the deeper trap during early 1990.Bacteria contr
ibuted 0.5-3.5% (mean = 2.0%) of POC flux at 3100 m, and at 4465 m the
y contributed 1-40% (mean = 11%) of the POC. Cyanobacteria contributed
up to 0.13% of POC at both trap depths. The substantial seasonal and
interannual variations in both bacterial and cyanobacterial fluxes may
be due to different seasonal and interannual growth patterns of the h
eterotrophic and phototrophic bacteria and/or different mechanisms of
inclusion in sinking particles in the upper ocean. The proportions of
bacterial and cyanobacterial production in surface waters arriving at
3100 m during the maximum flux of microorganisms were 1.5% and 0.26%,
respectively, and will be lower at other times of year. There was a si
gnificant positive correlation between % bacterial carbon and % partic
ulate organic carbon of the mass flux which may indicate that the high
er the bacterial concentration on sedimenting material the higher the
concentration of POC. Significant negative correlations also occurred
between C/N molar ratio and bacterial carbon flux. The material compri
sing the second major flux event in 1989 contained extremely high conc
entrations of bacteria and cyanobacteria, These observations may indic
ate that aggregates may escape solubilization in the upper water colum
n and arrive relatively fresh on the deep-sea bed, 74% of the annual t
otal of bacterial flux and 77% of the annual cyanobacterial flux, occu
rred within this short period (12%) of the investigation. There is evi
dence that the deeper trap received bacteria from resuspended sediment
s and colonized settled detritus and that there may be enhanced growth
of these deep sea bacteria through stimulation from a major mass flux
event. The annual bacterial flux was 1.1 x 10(12) cells/m(2)/annum wh
ich is equivalent to 56.3 mg bacterial carbon/m(2)/annum, around 4, 5
and 27.0 mg DNA, RNA and protein/m(2)/annum and 27.5 x 10(12) plasmid
encoded phenotypic genes/m(2)/annum, The supply of DNA and mechanisms
of transfer are potentially available for genetic exchange to occur be
tween populations previously assumed to be genetically isolated, that
of the bacteria in the surface waters and those in the deep-sea.