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Two research cruises (CIMAR 13 Fiordos) were conducted in the N–S oriented macrobasin of the Moraleda Channel (42–47°S), which includes the E–W oriented Puyuhuapi Channel and Aysen Fjord, during two contrasting productive seasons: austral winter (27 July–7 August 2007) and spring (2–12 November 2007). These campaigns set out to assess the spatio-temporal variability, defined by the local topography along Moraleda Channel, in the biological, physical, and chemical oceanographic characteristics of different microbasins and to quantify the carbon budget of the pelagic trophic webs of Aysen Fjord.
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Research papers
Seasonal plankton variability in Chilean Patagonia fjords: Carbon flow
through the pelagic food web of Aysen Fjord and plankton dynamics in the
Moraleda Channel basin
H.E. Gonza
´lez
a,b,c,d,
n
, L. Castro
b,c,e
, G. Daneri
b,c,d
, J.L. Iriarte
c,d,f
, N. Silva
g
, C.A. Vargas
d,h
,
R. Giesecke
c
,N.Sa
´nchez
a
a
Universidad Austral de Chile, Instituto de Biologı
´a Marina, Casilla 567, Valdivia, Chile
b
Centro COPAS de Oceanografı
´a, Universidad de Concepcio
´n, Casilla 160-C, Concepcio
´n, Chile
c
Centro BASAL COPAS Sur-Austral, Universidad de Concepcio
´n, Casilla 160-C, Concepcio
´n, Chile
d
Centro de Investigacio
´n de Ecosistemas de la Patagonia (CIEP), Bilbao 449, Coyhaique, Chile
e
Departamento de Oceanografı
´a, Universidad de Concepcio
´n, Casilla 160-C, Concepcio
´n, Chile
f
Universidad Austral de Chile, Instituto de Acuicultura, Casilla 1327, Puerto Montt, Chile
g
Escuela de Ciencias del Mar, Pontificia Universidad Cato
´lica de Valparaı
´so, Casilla 1020, Valparaı
´so, Chile
h
Centro de Ciencias Ambientales EULA-Chile, Unidad de Sistemas Acua
´ticos, Universidad de Concepcio
´n, Casilla 160-C, Concepcio
´n, Chile
article info
Article history:
Received 18 November 2009
Received in revised form
24 August 2010
Accepted 25 August 2010
Available online 8 September 2010
Keywords:
Chilean Patagonia
Fjord and channel ecosystems
Plankton dynamics
abstract
Two research cruises (CIMAR 13 Fiordos) were conducted in the N–S oriented macrobasin of the
Moraleda Channel (42–471S), which includes the E–W oriented Puyuhuapi Channel and Aysen Fjord,
during two contrasting productive seasons: austral winter (27 July–7 August 2007) and spring (2–12
November 2007). These campaigns set out to assess the spatio-temporal variability, defined by the local
topography along Moraleda Channel, in the biological, physical, and chemical oceanographic
characteristics of different microbasins and to quantify the carbon budget of the pelagic trophic webs
of Aysen Fjord.
Seasonal carbon fluxes and fjord-system functioning vary widely in our study area. In terms of
spatial topography, two constriction sills (Meninea and Elefantes) define three microbasins along
Moraleda Channel, herein the (1) north (Guafo-Meninea), (2) central (Meninea-Elefantes), and (3) south
(Elefantes-San Rafael Lagoon) microbasins. In winter, nutrient concentrations were high (i.e. nitrate
range: 21–14
mM) and primary production was low (153–310 mgC m
2
d
1
), suggesting that reduced
light radiation depressed the plankton dynamics throughout Moraleda Channel. In spring, primary
production followed a conspicuous N–S gradient, which was the highest (5167 mgC m
2
d
1
) in the
north microbasin and the lowest (742 mgC m
2
d
1
) in the south microbasin. The seasonal pattern of
the semi-enclosed Puyuhuapi Channel and Aysen Fjord, however, revealed no significant differences in
primary production ( 800 mgC m
2
d
1
), and vertical fluxes of particulate organic carbon were nearly
twice as high in spring as in winter (266 vs. 168 mgC m
2
d
1
).
At the time-series station (St. 79), the lithogenic fraction dominated the total sedimented matter
(seston). The role of euphausiids in the biological carbon pump of the Patagonian fjords was evident,
given the predominance of zooplankton fecal material, mostly euphausiid fecal strings (46% of all fecal
material), among the recognizable particles contributing to the particulate organic carbon flux.
The topographic constriction sills partially modulated the exchange of oceanic waters (Subantarctic
Surface Water) with freshwater river discharges along the Moraleda Channel. This exchange affects
salinity and nutrient availability and, thus, the plankton structure. The north microbasin was dominated
by a seasonal alternation of the classical (spring) and microbial (winter) food webs. However, in the
south microbasin, productivity was low and the system was dominated year-round by large inputs of
glacier-derived, silt-rich freshwater carrying predominantly small-sized diatoms (Skeletonema spp) and
bacteria. When superimposed upon this scenario, highly variable (seasonal) solar radiation and
photoperiods could exacerbate north–south differences along Moraleda Channel.
&2010 Elsevier Ltd. All rights reserved.
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/csr
Continental Shelf Research
0278-4343/$ - see front matter &2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.csr.2010.08.010
n
Corresponding author. Tel.: + 56 63 221559; fax: +56 63 221455
E-mail address: hgonzale@uach.cl (H.E. Gonza
´lez).
Continental Shelf Research 31 (2011) 225–243
1. Introduction
Fjords, estuaries, and other ‘‘semi-enclosed’’ coastal ecosys-
tems are among the most biogeochemically dynamic areas of the
biosphere (Gattuso et al., 1998). These systems transport and
exchange large amounts of organic matter and energy between
terrestrial and open-ocean environments and are key contributors
to the carbon fluxes of the coastal ocean (Walsh, 1991). Nutrient
and carbon cycling in fjords probably respond to changes in the
expected input of freshwater and organic matter via hydrological/
climatological fluctuations and/or human activities (e.g., agricul-
ture, forestry, aquaculture, etc.). The sustainable management of
fjord and estuarine systems in southern Chile necessitates a better
understanding of interactions between processes such as nutrient
and organic matter inputs, fjord–atmosphere CO
2
exchanges, and
carbon sequestration, and between these processes and the
environment. The Chilean Patagonia is located on the south-
eastern border of the Pacific Ocean and covers more than 1000 km
between 411and 551S. Fjords therein usually range between 100
and 500 m depth, from 10 to 70 km long, and have a two-layer
structure that is vertically limited by a strong halocline between 4
and 20 m depth (Silva et al., 1997; Ca
´ceres et al., 2002). In the area
covered by this study, both pluvial and nival seasonal regimes
modulate the freshwater input from rivers. Oceanographically,
this region constitutes a transitional marine system influenced by
deep oceanic waters with high salinity (431 psu) and elevated
nutrient loads (nitrate: 412
m
M; orthophosphate: 41.0
m
M) and
by low-salinity (o25 psu) surface freshwater. The estuarine
waters are relatively poor in dissolved inorganic nutrients (nitrate
and orthophosphate), and most nutrients are provided by oceanic
Subantarctic Waters (SAAW), as previously documented for the
southern Chile shelf margin (Silva and Neshyba, 1979; Silva et al.,
1997, 1998; Silva and Guzma
´n, 2006; Silva, 2008). The quasi-
permanent, low-salinity layer in the upper 5–10 m of the water
column imposes a strong barrier to (1) the mixing of inorganic
nutrients from the deeper, saltier oceanic layer (450 m depth),
(2) the export of phytoplanktonic carbon out of the euphotic layer,
and (3) the entrance of several zooplankton species of oceanic
origin (e.g., large copepods, euphausiids, etc.).
The primary production (PP) regime is reported to be highly
seasonal and may result in the efficient export of carbon to
sediments in spring (Gonza
´lez et al., 2010). Therefore, the Chilean
fjord region could be a major ‘‘CO
2
sink’’ during the productive
season (R. Torres et al., unpublished data). Thus, it is important to
understand the processes that modulate the efficiency of the
biological pump in this region (Sarmiento and Siegenthaler, 1992;
Pantoja et al., 2010) and at high latitudes where seasonality often
plays a pivotal role in structuring marine food webs and carbon
export production. In spring, the food web structure of the
Patagonian fjords is mainly sustained by large chain-forming
diatoms that are favored by increased solar radiation (Iriarte et al.,
2001), an extended photoperiod, a constant supply of silicic acid
(input via freshwater discharges), and orthophosphate and
nitrogen (provided by seawater below the pycnocline) (Silva
et al., 1997). Nanoplankton (both auto- and heterotrophic) largely
dominated the system in winter, resulting in the predominance of
the microbial loop (Gonza
´lez et al., 2010).
This study aims to assess the carbon budgets and flows in
winter and spring through the pelagic food webs of two highly
stratified semi-enclosed areas (Aysen Fjord and Puyuhuapi
Channel) and a large, N–S oriented basin (herein, Moraleda
Channel) from the Boca del Guafo passage to Elefantes Gulf. In
particular, we (1) establish the spatial/temporal variability of the
biological, physical, and chemical oceanographic characteristics of
different microbasins defined by the local topography, (2)
quantify the carbon budget of the pelagic trophic webs in Aysen
Fjord, and (3) assess the magnitude of particulate organic carbon
(POC) export below the halocline.
2. Materials and methods
Two research cruises (CIMAR 13 Fiordos) were carried out
during 2007 in the Chilean Patagonian fjords, covering two semi-
enclosed areas (Puyuhuapi Channel at 451S; Aysen Fiord at 461S),
both oriented E–W, and the large N–S oriented Moraleda Channel
(Fig. 1). These cruises were conducted in austral winter (27 July–7
August) and spring (2–12 November) on board the AGOR Vidal
Gorma
´z of the Chilean Navy. Two research approaches were
implemented:
(1) A transect of stations was covered along Moraleda Channel, as
were small transects along Puyuhuapi Channel and Aysen
Fjord. Water samples were collected from these stations at
discrete depths for bacteria, nano-, and microzooplankton
using a bottle–rosette system. The mesozooplankton samples
were collected by oblique tows with a Tucker trawl and WP-2
nets equipped with a flowmeter. The physical and chemical
structure of the water column (temperature, salinity, and
dissolved oxygen) was recorded with a CTD-O Seabird 19.
Salinity and oxygen sensors were calibrated by measuring
salinity (with an Autosal salinometer) and dissolved oxygen
(Winkler method) in discrete water samples (Table 1).
(2) A process-oriented time-series was maintained at a fixed
station (St. 79; 45122
0
S; 73104
0
W) within Aysen Fjord, where
we performed a carbon mass balance to study the flow and
fate of the photosynthetically generated carbon. For this, we
Fig. 1. Study area and stations (dots) along the transect from the Boca del Guafo
passage, along Moraleda Channel up to Elefantes Gulf, in the Chilean Patagonia.
The ‘‘circled dot’’ denotes the location of the ‘‘processes station’’ (St. 79) and the
Meninea and Elefantes constriction sills. The stations along Puyuhuapi Channel
(St. 84–87), Aysen Fjord (St. 76–81), and Estero Quitralco (St. 30, 31) are also
shown.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243226
Table 1
Parameter measured/estimated during the winter (W) and spring (S) cruises. *denotes the ‘‘process station’’ (St. 79).
Station number Water column
depth (m)
Lat. & Long. Chl (fractionated chlorophyll-a), POC (particulate organic carbon), BB (bacterial biomass), ANF-B (autotrophic nanoflagellate biomass), HNF-B (heterotrophic
nanoflagellate biomass), NUT (nitrate, phosphate, silicic acid), Microzoo-B (microzooplankton biomass), Cop-B (copepod biomass), Eup-B (euphausiid biomass),
HNF-G (heterotrophic nanoflagellate grazing), Microzoo-G (microzooplankton grazing), Cop-G (copepod grazing), Vert-F (vertical flux of particulates), and PP
(primary production).
Chl POC BB ANF-B HNF-B NUT Micro-zoo-B Cop-B Eup-B HNF-G Micro-zoo-G Cop-G Vert-F PP
Moraleda Channel
102 227 43146,40S74137,10W W,S W,S W,S W,S W,S W,S W,S W,S W,S W,S
103 196 43139,70S74117,30W W,S W,S W,S W,S W,S W,S W,S W,S W,S
33 210 43142,50S73151,00W W,S W,S W,S W,S W,S W,S W,S W,S W,S W,S
34 175 43148,00S73137,60W W,S W,S W,S W,S W,S W,S W,S W,S W,S
36 189 43158,50S73122,70W W,S W,S W,S W,S W,S W,S W,S W,S W,S
37 315 44113,60S73126,00W W,S W,S W,S W,S W,S W,S W,S W,S W,S
38 450 44126,50S73128,80W W,S W,S W,S W,S W,S W,S W,S W,S W,S
39 303 44139,70S73130,10W W,S W,S W,S W,S W,S W,S W,S W,S
40 197 44152,20S73130,40W W,S W,S W,S W,S W,S W,S W,S W,S
41 250 45106,90
S73138,90W W,S W,S W,S W,S W,S W,S W,S W,S W,S
43 65 45115,60S73139,60W W,S W,S W,S W,S W,S W,S W,S
45 120 45121,90S73139,10W W,S W,S W,S W,S W,S W,S W,S W,S
46 297 45130,80S73131,70W W,S W,S W,S W,S W,S W,S W,S W,S W,S
47 226 45143,10S73133,80W W,S W,S W,S W,S W,S W,S W,S W,S W,S
48 128 45152,50S73135,60W W,S W,S W,S W,S W,S W,S W,S W,S W,S
49 58 46103,90S731138,10W W,S W,S W,S W,S W,S W,S W,S
50 62 46111,40S731140,10W W,S W,S W,S W,S W,S W,S W,S
51 10 46119,00S731143,00W W,S W,S W,S W,S W,S W,S W,S
52 123 46126,00S73146,00W W,S W,S W,S W,S W,S W,S W,S W,S W,S
Puyuhuapi Channel
84 310 44156,30S73116,20W W,S W,S W,S W,S W,S W,S W,S
85 234 44153,00
S73102,10W W,S W,S W,S W,S W,S W,S W,S
86 270 44147,00S72152,50W W,S W,S W,S W,S W,S W,S W,S W,S
87 267 44139,30S72144,60W W,S W,S W,S W,S W,S W,S W,S
Aysen Fjord
76 337 45122,90S73131,90W W,S W,S W,S W,S W,S W,S W,S W,S W,S
77 220 45119,60S73119,70W W,S W,S W,S W,S W,S W,S W,S W,S W,S
78 338 45117,00S73110,40W W,S W,S W,S W,S W,S W,S W,S W,S W,S
79*324 45122,10S73104,20W W,S W,S W,S W,S W,S W,S W,S W,S W,S W,S W,S W,S W,S W,S
80 198 45126,20S72156,70W W,S W,S W,S W,S W,S W,S W,S W,S W,S
81 165 45124,00S72150,60W W,S W,S W,S W,S W,S W,S W,S W,S
Estero Quitralco
30 75 45146,00S73128,50W W,S W,S W,S W,S W,S W,S W,S
31 230 45140,00S73116,00W W,S W,S W,S W,S W,S W,S W,S
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 227
estimated size-fractionated PP, micro-, and mesozooplankton
grazing, and the vertical carbon flux. In addition, we
determined the abundance and carbon-based biomass of
phytoplankton, bacteria, auto- and heterotrophic nanoflagel-
lates, and microzooplankton (i.e., tintinnids, dinoflagellates,
and copepod nauplii).
2.1. Nutrients
We analyzed nutrient concentrations (nitrate, orthophosphate,
and silicic acid) using water samples collected from all stations at
depths of 1, 5, 10, 25, 50, 75, 100, 150, 200, 250, 300, 350, and
400 m, depending on the water depth at each station. Samples
were taken using a CTD-rosette equipped with 24 Niskin bottles.
Water samples (50 mL) were stored at –20 1C in acid-cleaned,
high-density polyethylene bottles and analyzed in a nutrient
autoanalyzer (Mod. Technicon) according to Atlas et al. (1971).
2.2. Particulate organic carbon
Water samples (0.5–1.0 L) were collected at 0, 10, 25, and 50 m
depth to determine POC concentrations in the water column.
These samples were filtered through precombusted 0.7
m
m MFS
filters, then frozen and stored for later elemental analysis. POC
measurements were conducted with a Europa Hydra 20-20
continuous flow isotope ratio mass spectrometer after combus-
tion at 1000 1C at the UC Davis Stable Isotope Facility Laboratory
(USA); acetanilide was used as the standard (Bodungen et al.,
1991).
2.3. Bacteria abundance and biomass
Sub-samples (20 mL) for the enumeration of heterotrophic
bacteria were collected at selected depths (0, 5, 10, 25, 50 m),
preserved with 0.22
m
m pre-filtered glutaraldehyde (2% final
concentration), and stored in the dark at 5 1C. From each sample,
2 mL was stained with fluorochrome DAPI (4
0
,6-diamino-2-
phenylindole; 100
m
LmL
1
final concentration) (Porter and Feig,
1980) on polycarbonate membrane filters (Nuclepore, 0.2
m
m)
and counted using an epifluorescence Zeiss Axiovert microscope
at 1000 magnification. More than 100 cells were counted from
20 random fields for each filter. Bacterial biomass was estimated
using a factor of 20 fgC cell
1
(Lee and Fuhrman, 1987).
2.4. Phytoplankton abundance, chlorophyll-a, biomass, and primary
production
We collected sub-samples (300 mL) at selected depths (0, 5,
10, and 25 m) and fixed them in acid Lugol’s solution (1% final
concentration) for diatom counts. An aliquot of 50 mL was taken
from each subsample and placed in a settling chamber for 30 h
prior to analysis under an inverted microscope (Zeiss Axiovert
200, 400 magnifications). Standard counting methods were
used (Uterm¨
ohl, 1958), and a carbon:plasma volume ratio of
0.11 pgC
m
m
3
was applied for diatom carbon estimations (Edler,
1979). Size-fractionated chlorophyll-a(Chl-a) was measured at
each sampling station in three sequential steps: (1) for the
nanoplankton fraction (2.0–20
m
m), seawater (125 mL) was pre-
filtered using a 20
m
m Nitex mesh and collected on a 2.0
m
m
Nuclepore filter; (2) for the picoplankton fraction (0.7–2.0
m
m),
seawater (125 mL) was pre-filtered using a 2.0
m
m Nuclepore and
collected on a 0.7
m
m MFS glass fiber filter; and (3) for the whole
phytoplankton community, seawater (125 mL) was filtered
through a 0.7
m
m MFS glass fiber filter. The microphytoplankton
fraction was obtained by subtracting the Chl-aestimated in
steps 1 and 2 from the Chl-aestimated in step 3. Filters were
immediately frozen (–20 1C) until later fluorometric analysis,
using acetone (90% v/v) for the pigment extraction (Turner Design
TD-700), according to Parsons et al. (1984).
2.5. Size-fractionated primary production
Water samples were collected with a 5 L Go-Flo PVC bottle at
four depths – the surface, the subsurface Chl-amaximum, 40%
light penetration, and the lower limit of the photic layer (1% light
penetration) – as proposed by Steemann-Nielsen (1952). Samples
for PP determinations were incubated in 100 mL borosilicate glass
bottles (two clear replicate bottles and one dark bottle for each
depth) in a natural-light incubator for 4 h (usually 10:00–14:00).
The temperature was regulated by running surface seawater over
the incubation bottles. For the four incubation depths (surface,
subsurface Chl-amaximum, 40%, and 1% light penetration), light
intensity was attenuated using a screen to mimick the light at the
water collection depth. Sodium bicarbonate (40
m
CiNaH
14
CO3)
was added to each bottle. Samples were handled under subdued
light conditions prior to and after the incubation periods.
Following incubation, the contents were filtered according to
the fractionation procedures used for Chl-a. Filters (0.7 and
2.0
m
m) were placed in 20 mL borosilicate scintillation vials and
kept at –20 1C until reading. To remove excess inorganic carbon,
the filters were treated with HCl fumes for 4 h. A cocktail (10 mL,
Ecolite) was added to the vials and radioactivity was determined
in a scintillation counter (Beckman). Depth-integrated values of
PP (mgC m
2
h
1
) were calculated using trapezoidal integration
over the euphotic zone and considering the four depths
mentioned above. Integrated production rates per hour were
multiplied by daily light hours for Aysen Fjord. The relationship
between depth-integrated PP (mgC m
2
d
1
) and total Chl-a
(mg m
2
) (PP:Chl-aratio) was used as a relative proxy for diatom
‘‘health’’ (physiological condition), assuming that the higher the
ratio, the better the diatom condition.
2.6. Nanoflagellate and microzooplankton abundance
Sub-samples (20 mL) of nanoflagellates (auto- and hetero-
trophs) were filtered with a 0.8
m
m black polycarbonate mem-
brane filter and stained with proflavine (0.033% w/v in distilled
water) according to Haas (1982), then fixed with glutaraldehyde.
Counts of each filter were done with epifluorescence microscopy
(1000 magnification), and at least 50 cells were counted from
50 random fields.
For dinoflagellate, tintinnid, and crustacean nauplius counts,
10–30 L of seawater from different depths (surface, 5, 10, 25, and
50 m) was carefully and gently filtered through a sieve (10
m
m
mesh size), then concentrated up to a final volume of 100 mL
and preserved with buffered formalin (5% final concentration).
Carbon to plasma volume ratios of 0.3 and 0.19 pgC
m
m
3
were
used for heavily thecate and athecate dinoflagellate forms,
respectively (Lessard, unpublished data fide Gifford and Caron,
2000), and 0.148 pgC
m
m
3
was applied for ciliates (Ohman and
Snyder, 1991). Counts were done using standard methods
(Uterm¨
ohl, 1958).
2.7. Nanoflagellate and microzooplankton grazing experiments
These experiments were performed using the size-fractiona-
tion method (Verity, 1986; Kivi and Setala, 1995). Water samples
were collected from the fluorescence maximum depth with a
clean 10 L GoFlo bottle–rosette system. After collection, seawater
was size-fractionated by reverse filtration into three fractions: (1)
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243228
o2
m
m (i.e., mostly bacteria and cyanobacteria), (2) o10
m
m
(i.e., mostly bacteria, cyanobacteria, phototrophic (PNF), and
heterotrophic (HNF) nanoflagellates), and (3) o115
m
m (i.e., the
whole photo-heterotrophic community). Grazing rates were
calculated by comparing prey growth rates in the presence and
absence of predators selected by reverse filtration, comparing (1)
and (2) for HNF grazing, and (2) and (3) for microzooplankton
(ciliates+ dinoflagellates) grazing on nanoflagellates (both PNF
and HNF) (Gifford, 1993). The procedures and methods are fully
described and published elsewhere (Vargas et al., 2008).
2.8. Mesozooplankton abundance and grazing rates
Samples were collected day and night by oblique tows using a
Tucker trawl net (catch area: 1 m
2
, mesh size: 300
m
m), equipped
with a calibrated flowmeter at two depths (0–25 and 25–50 m).
Additional tows using a WP-2 (mesh size: 200
m
m) were done to
collect small calanoid copepods. Samples were preserved in borax
buffered formalin (10% final conc.) for later analyses of dominant
zooplankton groups.
To estimate copepod grazing, animals were collected by slow
vertical hauls in the upper 20 m of the water column using a WP-2
net (mesh size: 200
m
m) with a large, non-filtering cod end (40 L).
Undamaged copepods were placed in 500 mL (4–8 small copepods)
or 1000 mL (2–3 large copepods) acid-washed polycarbonate
bottles. These bottles were filled with ambient water loaded with
natural food assemblages of microplankton pre-screened through a
200
m
m net to remove most grazers. Three control bottles without
animals and three bottles with two to four animals each were placed
in an incubator rack on deck for approximately 19–25 h. The
seawater incubation was mixed by hand every hour and, to some
extent, by the ship’s motion. Initial control bottles were immediately
preserved with 2% acid Lugol’s solution and a subsample was
preserved in glutaraldehyde. At the end of the incubation, sub-
samples were taken from all bottles and preserved in glutaraldehyde
(20 mL) for nanoflagellate counts and in acid Lugol’s solution
(60 mL) for cell concentrations. Clearance and ingestion rates,
measured as cell removal, were calculated according to Frost
(1972) as modified by Marin et al. (1986).
The vertical flux of POC was estimated using surface-tethered,
quadruple cylindrical sediment traps (modified from Grundersen,
1991) with a capture area of 50 cm
2
and an aspect ratio of 8.3
each. Traps were deployed at the halocline (25 m) and at 50 m
water depth at the ‘‘process station’’ for periods ranging from 43.2
to 50.4 h in August and 26.4 to 45.6 h in November 2007. Sub-
samples were used for microscopy following standard analysis
(Uterm¨
ohl, 1958). Measurements of POC in the sediment trap
samples were done as for the water column samples.
Data were subjected to a full factorial two-way ANOVA
(salinity/temperature vs. basin and season and basin seasons)
with a subsequent Tukey HSD post hoc test of the differences
between means (
a
¼0.05; Sokal and Rohlf, 1981).
3. Results
3.1. Environmental conditions
3.1.1. Moraleda Channel
The water temperature varied considerably along the transect for
the two sampling seasons. In winter, a quasi-homothermal (9.0–
9.3 1C) vertical distribution was recorded between the Boca del
Guafo passage and the Meninea constriction sill (St. 102–43),
interrupted only by intrusions of warmer water (9.5 1C) at
100 m depth from both sides of the constriction sill and by the
inflow of cold surface water ( o8.4 1C) from Puyuhuapi Channel.
South of the Meninea constriction sill, a subsurface ( 430 m)
increase in temperature was noticed beneath the cooler surface
layer (8.9–9.3 1C), promoting the formation of an inverted thermo-
cline. Further south, the shallow constriction sill (St. 50; 25 m
depth) at Elefantes Gulf formed a small, shallow basin with low
temperatures from the surface to the bottom (7.8–8.3 1C).
In spring, temperatures were the highest at the surface
(10.0–10.7 1C), with a weak subsurface thermocline. From the
Boca del Guafo passage, the thermocline rose from 60 m up to
20 m depth on the southern side of the Meninea constriction sill,
whilst weakening further south, where a vertical, quasi-homo-
geneous thermal distribution (9.4 1C) was found. In the north-
ern section of Moraleda Channel, a cold tongue (8.0–8.3 1C) of
deep water (150 m depth) penetrated from the Boca del Guafo
passage to Moraleda Channel. As in winter, water temperatures
between the Meninea and Elefantes constriction sills increased
slightly (as compared with the northern section), remaining
approximately constant down to the bottom (9.2–9.4 1C). South of
the Elefantes constriction sill, the temperature dropped to 8.6 1C
and remained constant throughout the entire water column
(Fig. 2a and d).
In winter and spring, latitudinal gradients in salinity were
evident, forming three distinct microbasins enclosed by bottom
topography. (1) In the north microbasin, the intrusion of oceanic
waters into Moraleda Channel resulted in higher salinities
(34 psu) at the bottom that decreased slightly (33 psu) towards
the surface. (2) In the central microbasin, salinity decreased
slightly (31 psu) at the bottom, and a low-salinity surface tongue
(27 psu) was observed moving northward. (3) Finally, fresh-
water discharges from the San Rafael Lagoon and meltwater from
the Northern Ice Field drain into the south microbasin of
Moraleda Channel, constituting a small, low-salinity ( 22%)
basin. The intense vertical gradients of salinity (as opposed to
temperature) determined the density gradients of the entire
transect and the vertical and horizontal physical and chemical
structures of the three basins. From St. 52, a tongue of less saline
water close to the surface (o40 m depth) moved northwards
towards the Elefantes (24 psu) and Meninea (29 psu) constric-
tions (Fig. 2b and e).
An ANOVA analysis of mean temperature showed significant
differences between the three basins, the two seasons, and
between basins and seasons (Table 2). In spring, the highest
mean temperatures were recorded in the central basin
(9.470.01 1C), whereas the lowest temperatures were always
measured in the south basin (8.770.03 1C). In winter, the mean
temperature in Moraleda Channel was slightly lower than in
spring (9.370.01), and temperatures increased further south of
the Meninea constriction sill (9.670.01). As in spring, the south
microbasin displayed the lowest temperatures (8.170.04
o
C). The
ANOVA for the mean salinity revealed significant differences
between almost all parameters investigated. Overall, the mean
salinity decreased from north to south (from basin 1 to 3) in both
seasons, with significant differences between basins within
seasons. Among seasons, only the central basin showed significant
differences. Salinity was the highest along Moraleda Channel in
spring (33.3 psu) and winter (33.2 psu), but decreased slightly
(down to 30.4 psu) in the central microbasin in both seasons.
Salinity was the lowest (23.3 psu) in the south microbasin in
spring and winter.
3.1.2. Puyuhuapi Channel
In winter, the surface temperature decreased gradually from
the head (9 1C) to the mouth of the fjord (7.6 1C). A shallow
inverted thermocline (10 m depth) at the head of the fjord
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 229
deepened to 25 m at the mouth, associated with a thermal
increase (9.5–10.5 1C) between 50 and 140 m depth at the fjord
head. This deep intrusion of warm water could be clearly
observed throughout the entire fjord, as could the gradual
decrease in temperature from the head (10.5 1C) to the mouth
(9.7 1C) of the fjord (Fig. 3a). A spring thermocline (10–11 1C) was
observed in the upper 10 m along the entire fjord. Close to the
head of the fjord, an intrusion of warm (9.7–10 1C) subsurface
(40–110 m depth) water flowed towards the mouth, where it
disappeared close to St. 85. At the mouth of the fjord, an intrusion
of cold water (91C) at 100 m depth penetrated up to St. 85,
where it gradually deepened, disappearing towards the head of
the fjord (Fig. 3d). The freshwater input in the upper 10 m
promoted a strong halocline with a surface salinity gradient
increasing from the head (21 psu) of the fjord to its mouth
(26 psu). Under the strong halocline, a vertical salinity gradient
(31–32 psu) was observed between 20 and 100 m depth. Below
this, an almost continuous salinity gradient (vertical and
horizontal) was evident. In winter, surface salinities ranged
between 28.8 and 30 psu along the fjord, interrupted by the
intrusion of colder (7.5 1C), fresher (25 psu) water at St. 85.
The halocline deepened from the fjord’s head ( 10 m) towards its
mouth (25 m). Under the halocline, salinity increased from 32
to 34 psu, remaining constant throughout the entire fjord (Fig. 3b
and e). Density followed a similar spatial pattern as salinity
(Fig. 3c and f).
3.1.3. Aysen Fjord
In winter, a strong inverted thermocline was observed from
51C at the surface of the fjord’s head to 10 1C at 20 m depth.
Towards the mouth of the fjord, surface temperatures (o30 m)
ranged from 9.3 to 9.7 1C and an intrusion of slightly warmer
(10.7–11.0 1C) subsurface water was observed between 50 and
140 m depth. Below 200 m depth, the temperature fell to 9.7 1C
(Fig. 3g).
In spring, we observed an inverted thermocline with lower
temperatures (9.5–9.9 1C) at the surface ( o50 m), followed by an
intrusion of warmer water (410.7 1C) between 50 and 130 m
depth from the head of the fjord to the mouth (up to St. 78)
(Fig. 3j). In winter, the vertical structure showed a strong
halocline (from 8.5 to 29 psu) and salinities below 55 m depth
remained 31.5 psu (Fig. 3h). In spring, maximum gradients
occurred at the head of the fjord, where surface salinity decreased
down to 2%. A quasi-homohaline layer (31.5 psu) was found from
75 m depth down to the bottom (Fig. 3k). The freshwater
influence was noticed up to the mouth of the fjord, with some
breaks where freshwater and seawater mixed, resulting in
salinities 28 psu. As in Puyuhuapi Channel, the vertical density
structure was defined by salinity (Fig. 3i and l).
3.2. Nutrient concentrations (NO
3
,PO
3
4
, Si(OH)
4
)
In winter and spring, the average integrated salinity concen-
tration for the upper 25 m water column showed a strong N–S
gradient within Moraleda Channel, with values fluctuating from
33 psu in the north microbasin to 28 psu in the central microbasin
and 22 psu in the south microbasin. The ranges were less
pronounced in Puyuhuapi Channel, Aysen Fjord, and Estero
Quitralco (28–30 psu) (Fig. 4, upper panel). In winter, nitrate
and phosphate concentrations mimicked salinity, decreasing
Table 2
Multifactorial ANOVA analysis between basins (northern, central, and southern
Moraleda Channel) and seasons (Winter and Spring).
Test Value FEffect
df
Error
df
p
Intercept Wilks 0.002557 1,247,371 2 6395 0.000000
Winter–Spring Wilks 0.995860 13 2 6395 0.000002
Basin Wilks 0.167182 4623 4 12,790 0.000000
Winter–Spring-
Basin
Wilks 0.969928 49 4 12,790 0.000000
Fig. 2. Vertical distribution of temperature (1C), salinity, and density (
s
t
) along the transect from the Boca del Guafo passage to Elefantes Gulf in winter (a, b, c) and spring
(d, e, f).
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243230
along Moraleda Channel from the Boca del Guafo passage (21 and
1.5
m
M, respectively) to Elefantes Gulf (14 and 1.2
m
M, respec-
tively) (Fig. 4). On the contrary, silicic acid increased in winter
from the Boca del Guafo passage to Elefantes Gulf (7.5–28.3
m
M).
The Si(OH)
4
:NO
3
ratio increased four-fold from the northern (0.5)
to the southern (2) stations along the transect (Fig. 4). In spring, a
Fig. 3. Vertical distribution of temperature (1C), salinity, and density (
s
t
) along the transect in Puyuhuapi Channel in winter (a, b, c) and spring (d, e, f), and in Aysen Fjord in
winter (g, h, i) and spring (j, k, l).
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 231
0
5
10
15
20
25
Moraleda Channel Puyuhuapi
Channel
Aysen
Fjord
NO3 (µM)
0.0
0.5
1.0
1.5
2.0
2.5
PO4 (µM)
0
10
20
30
40
50
60
Si(OH)4 (µM)
102
0
2
4
6
8
10
7684 30
Stations
Si(OH)4 / NO3
De
p
th (m)
-400
-300
-200
-100
0
Salinity (PSU)
20
22
24
26
28
30
32
34
36
Winter
Spring
10333 34 36 37 38 39 40 41 43 45 46 47 48 49 50 51 52 858687 77 78 79 80 81 31
102 7684 3010333 34 36 37 38 39 40 41 43 45 46 47 48 49 50 51 52 858687 77 78 79 80 81 31
102 7684 3010333 34 36 37 38 39 40 41 43 45 46 47 48 49 50 51 52 858687 77 78 79 80 81 31
7684 30858687 77 78 79 80 81 31
102 7684 3010333 34 36 37 38 39 40 41 43 45 46 47 48 49 50 51 52 858687 77 78 79 80 81 31
Estero
Quitralco
5251504948474645434140393837363433103
Fig. 4. From top to bottom panels: integrated average values of salinity in winter (black dots) and spring (open dots) with the bottom topography (grey areas in meters)
along Moraleda Channel, Puyuhuapi Channel, Aysen Fjord, and Estero Quitralco. Average concentrations in the upper 25 m of the water column for nitrate (NO
3
,
m
M), silicic
acid (Si(OH)
4
,
m
M), and phosphate (PO
4
,
m
M) and the Si(OH)
4
/NO
3
ratio at the same locations. Vertical bars denote standard error.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243232
Fig. 5. (a) Integrated (upper 25 m water column) concentrations of particulate organic carbon (POC), chlorophyll-a(Chl-a) and carbon biomasses for bacteria and
heterotrophic nanoflagellates (HNF), along Moraleda Channel, Puyuhuapi Channel, Aysen Fjord, and Estero Quitralco in the winter and spring sampling periods. All data are
given in mgC m
–2
except Chl-a(mg Chl-am
–2
). Factors of 20 fgC cell
1
and 6.5 pg cell
1
were used for bacteria (Lee and Fuhrman, 1987) and nanoflagellates (Børsheim and
Bratbak, 1987). (b). As in a, but for autotrophic nanoflagellates (ANF), microzooplankton (microzoo), and mesozooplankton (mesozoo). For carbon transformations, the
same factors were used as in Figs. 7 and 8.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 233
ca. four-fold reduction in all nutrient concentrations occurred in
the north microbasin, whereas the concentrations in the central
and south microbasin remained similar. Puyuhuapi Channel also
showed lower values for all nutrients in spring, but in Aysen Fjord,
only nitrate decreased and no changes were noted in the Estero
Quitralco between campaigns (Fig. 4).
3.3. Particulate organic carbon
Integrated POC concentrations in the upper 25 m of the water
column during contrasting seasons showed a similar pattern to
Chl-a, being higher in the northern section of Moraleda Channel
up to the Meninea constriction sill and drastically decreasing
further south. In winter, mean POC in the northern section was
slightly higher (34257862 mg m
2
) than in the southern section
(25007318 mg m
2
), whereas the highest POC values were
measured in Puyuhuapi (5700 mg m
2
). In spring, the mean
POC in the northern section was 583271732 mg m
2
, decreasing
further south to 36797532 mg m
2
. The POC values were the
highest in Aysen Fjord (13,112 mg m
2
) and POC concentrations
in Puyuhuapi and Estero Quitralco were similar to those of the
Moraleda Channel stations. From winter to spring, a ca. two-fold
increase of POC was observed (Fig. 5a).
3.4. Chlorophyll-a
Total Chl-aand phytoplankton abundances showed marked
seasonal differences. In winter, the integrated Chl-aconcentra-
tions for the upper 25 m of the water column oscillated between 5
and 56 mg m
2
, whereas the spring range was 8.5–165 mg m
2
;
for both periods, values were the highest at the stations in
Puyuhuapi Channel (Fig. 5a). Picophytoplankton (o2
m
m) made
the greatest contribution of all the size-fractions to the total Chl-a
in winter for Moraleda Channel and Aysen Fjord, with mean
values of 9.675.4 and 8.775.3 mg m
2
, respectively, accounting
for 64% of the total Chl-acontent (Fig. 6). Large phytoplankton
cells (420
m
m) dominated in Puyuhuapi and Estero Quitralco,
reaching 34 and 38 mg Chl-am
2
, respectively, contributing to
71% and 83% of the total Chl-a. In spring, the total Chl-awas
clearly dominated by large phytoplankton cells ( 420
m
m) at
most sampling stations, with a mean of 32.3722.1 mg m
2
and
accounting for 51% of the total Chl-a(Fig. 6). This size fraction
consisted mainly of large diatoms that reached abundances of
810
8
and 2 10
10
cel m
2
, exceeding the winter range
(1 10
7
–6 10
9
cel m
2
) by up to one order of magnitude.
In winter and spring, total integrated Chl-adisplayed a
consistent spatial distribution pattern with two distinct zones:
from the Boca del Guafo passage to the mouth of Aysen Fjord
(high Chl-a) and between the Meninea constriction sill and
Elefantes Gulf (low Chl-a). In winter, the Chl-avalues in the
northern section ranged between 12 and 31 mg Chl-am
2
(mean
and s.d. of 1876 mg Chl-a m
2
) whereas in the south of the
Meninea constriction, Chl-aoscillated between 3 and 20 mg Chl-
am
2
(976 mg Chl-am
2
). In spring, the respective Chl-a
concentrations for the northern and southern sections ranged
from 33 to 102 mg m
2
(66726 mg m
2
) and 9 to 34 mg m
2
(2279mgm
2
)(Fig. 5a).
3.5. Bacterial abundance and biomass
The bacterial abundance in winter was relatively homoge-
neous at the stations in the study area, ranging between 1 and
210
5
cells mL
1
. The mean integrated abundance in the upper
layer (to 25 m depth) was 7.2 10
12
cells m
2
, equivalent to a
biomass of 144 mgC m
2
. The highest abundances were recorded
Fig. 6. Size-fractionated chlorophyll-aconcentration (mg m
–2
) integrated in the upper 25 m of the water column and differentiated by picoplankton (o5
m
m), nanophytoplankton (5–20
m
m), and microphytoplankton
(420
m
m) along Moraleda Channel, Puyuhuapi Channel, Aysen Fjord, and Estero Quitralco in the winter and spring sampling periods.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243234
Fig. 7. Integrated carbon biomass of heterotrophic (HNF) and autotrophic (ANF) nanoflagellates (upper panels) and microzooplankton integrated carbon biomass differentiated by dinoflagellates, tintinnids, and copepod nauplii
(lower panels) along Moraleda Channel, Puyuhuapi Channel, Aysen Fjord, and Estero Quitralco in the winter and spring sampling periods. For carbon transformations, the following equations were used: nanoflagellates
6.5 pg cell
1
(Børsheim and Bratbak, 1987), tintinnids (Verity and Langdon 1984), and copepod nauplii (Uye et al., 1996); carbon to plasma volume ratios were 0.3 pg C
m
m
3
for heavily athecate dinoflagellates and
0.19 pg C
m
m
3
for athecate dinoflagellates (Lessard unpublished data fide Gifford and Caron 2000). nd ¼no data.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 235
in Puyuhuapi Channel, with 11.3 10
12
cells m
2
and 226 mgC
m
2
(Fig. 5a). In spring, bacterial biomass was closely coupled to
the spatial distribution of phytoplankton and POC (Fig. 5a).
Bacterial abundances were the highest at St. 102 (20 10
12
cells
m
2
; 397.5 mgC m
2
) and decreased toward the Meninea
Channel (10–15 10
12
cells m
2
; 200–300 mgC m
2
). South of
the Meninea constriction sill, extending over Aysen Fjord and
Estero Quitralco, bacterial biomass decreased to 7 and 8 10
12
cells m
2
(140–160 mgC m
2
).
3.6. Nanoflagellate biomass
In winter, the biomasses of HNF and ANF were the highest from
the Boca del Guafo passage to the Moraleda Channel entrance
(St. 102–37): 94716 mgC m
2
for HNF and 55715 mgC m
2
for
ANF. Further south, along Moraleda Channel and in Puyuhuapi
Channel and Aysen Fjord, nanoflagellate biomasses remained
relatively constant (44711 mgC m
2
for HNF; 23711 mgC m
2
for ANF) except for a conspicuous increase at St. 86 (79 and
51 mgC m
2
, respectively).
In spring, ANF and HNF biomasses increased two-fold relative to
winter. In addition, the ANF biomass in spring was greater than the
HNF biomass (Fig. 5a and b). Unlike in winter, no clear spatial
distribution pattern was observed for the total spring nanoflagellate
biomass, which ranged from 36 to 214 mgC m
2
(103744 mgC
m
2
) for ANF and from 56 to 223 mgC m
2
(128741 mgC m
2
)for
HNF (Fig. 5a and b and Fig. 7 upper panel).
3.7. Microzooplankton
In winter, microzooplankton carbon came mainly from dino-
flagellates along Moraleda Channel, with a minor contribution by
tintinnids. Total biomass along the entire transect was low,
ranging between 0.2 and 8 mgC m
2
(1.572 mgC m
2
). Overall,
the microzooplankton biomasses recorded in the channels and
fjords were higher than those recorded along Moraleda Channel.
Along Puyuhuapi Channel, the tintinnid and dinoflagellate
biomasses increased significantly, exceeding 10 mgC m
2
; dino-
flagellates were the dominant taxa. In Aysen Fjord, the biomass
was slightly higher than in Moraleda Channel and was dominated
by tintinnids, whereas at the Estero Quitralco, microzooplankton
ranged between 4 and 8 mgC m
2
and dinoflagellates were the
dominant taxa.
In spring, the microzooplankton biomass increased substan-
tially (1637148 mgC m
2
) due to the presence of copepod
nauplii, which made up ca. 90% of the total biomass. The biomass
was the highest at the Boca del Guafo passage (3067175 mgC
m
2
) and along Aysen Fjord (2367196 mgC m
2
), then de-
creased gradually along Moraleda Channel from north to south,
being the lowest in Elefantes Gulf (Figs. 5b and 7lower panel).
3.8. Mesozooplankton
Copepods dominated the mesozooplankton abundance in both
spring and winter, with the euphausiid Euphausia valentini
making up most of the biomass. High mesozooplankton
biomass was always recorded at the entrance of Moraleda
Channel (4300 mgC m
2
), whereas the remaining stations
usually displayed abundances under 60 mgC m
2
. Samples were
taken during daylight hours at several stations, thus, the
euphausiid abundance may be underestimated at those stations
(Figs. 5b and 8).
Fig. 8. Integrated carbon biomasses of dominant copepod taxa and the euphausiid E. vallentini along Moraleda Channel, Puyuhuapi Channel, Aysen Fjord, and Estero Quitralco in the winter and spring sampling periods.
Neocalanus spp. 219
m
g C ind
1
(Ohman 1987, modified by Hirst et al. (2003)), Paracalanus spp. 5.1
m
g C ind
1
(Uye and Shibuno, 1992), Acartia spp. 6.4
m
g C ind
1
(Durbin et al., 1983), Calanus spp. 56
m
g C ind
1
(Escribano and
Rodrı
´guez, 1995), Rhincalanus nasutus 150
m
g C ind
1
(Huntley and Lopez, 1992), Centropages spp. 10
m
g ind
1
(Peterson et al., 1990), and E. valentini 5356
m
g C ind
1
(Sa
´nchez, unpublished). The stars denote samples taken
during daylight. nd¼no data.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243236
Fig. 9. Size-fractionated primary production (mgC m
–2
d
–1
), differentiated by picophytoplankton (o2
m
m), nanophytoplankton (2–20
m
m), and microphytoplankton
(420
m
m) (bars) and the PP:Chl-aratio in winter and spring (open dots) at three stations in the north, central, and south microbasins along Moraleda Channel (St. 102, 38,
52), one station in Puyuhuapi Channel (St. 86), and one station in Aysen Fjord (St. 79). The pie graphs show the relative contribution of dominant diatom taxa (species,
genera) to the total diatom assemblages in winter and spring at the same stations.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 237
3.9. Primary production and phytoplankton composition
In winter, integrated PP decreased from north to south, from
298 to 310 mgC m
2
d
1
at St. 102 and 38, respectively, to
153 mgC m
2
d
1
in Elefantes Gulf (St. 52). Picophytoplankton
(o2
m
m) contributed the most to the PP (40–45%) at the oceanic
station (St. 102) and at the entrance to Moraleda Channel
(St. 102–38), where the scarce large diatoms Eucampia spp. and
Coscinodiscus spp. were dominant. In Elefantes Gulf (St. 52), the
low levels of PP were largely sustained by nano- and micro-
phytoplankton, accounting for 40% and 35% of the total PP. This
station was mainly dominated by Skeletonema spp., which
contributed 80% of the total diatom abundance (Fig. 9). At
St. 79, the highest levels of PP (825.5 mgC m
2
d
1
) were
observed; these were mainly supported by nano- and micro-
phytoplankton, each contributing 38% to the total PP. At this
station, the diatoms were dominated by Thalassiosira spp. and
Skeletonema spp., which made up 80% of the total abundance.
In spring, the PP at the northern station (St. 102) was
extremely high (5167 mgC m
2
d
1
) and was accounted for-
mainly microphytoplankton (420
m
m), which made up 62% of
the total PP. The area covering St. 102–38 was almost exclusively
dominated by the diatom Guinardia spp. In the southern section of
Moraleda Channel, PP decreased from 1854 to 742 mgC m
2
d
1
at St. 38 to 52, respectively. At these two stations, PP was mainly
supported by nanophytoplankton (40–45% of total PP), with high
biomasses of the diatom genera Guinardia (St. 38) and Skeletone-
ma (St. 52). At St. 79, the mean PP was 831 mgC m
2
d
1
and
nanophytoplankton was the major contributor with 50% of the
total PP. In winter, the PP:Chl-aratio, a proxy of phytoplankton
activity, showed no clear spatial pattern along Moraleda Channel,
oscillating between 20 and 30. However, the semi-enclosed areas
close to the freshwater sources (Puyuhuapi Channel, Aysen Fjord,
and Elefantes Gulf) showed higher PP:Chl-aratios, fluctuating
between 50 and 70. In spring, the ratio decreased from the north
(60) to the south (30) microbasin along Moraleda Channel and
was also low in Puyuhuapi Channel (5) and Aysen Fjord (20)
(Fig. 9).
3.10. Ingestion rates of HNF micro- and mesozooplankton
The HNF abundance at St. 79 increased by 30% and that of bacteria
almost doubled from winter to spring. In winter, feeding rates among
experiments ranged between 5.3 and 9.2 bact HNF
–1
h
–1
,whereasthe
springtime feeding rates were relatively constant, ranging between 1
and 1.3 bact HNF
–1
h
–1
. We used the bacterial carbon conversion
and the HNF abundance to estimate the amount of carbon consumed
by the HNF per day (Table 2). In winter, HNF consumed
30.2 mgC m
2
d
1
, but in spring, they consumed three times less
(9.5 mgCm
2
d
1
).
In winter, the microzooplankton (o200
m
m) biomass at St. 79
was dominated by dinoflagellates and tintinnids, whereas in spring, a
drastic increase in copepod nauplii generated an increase of up to two
orders of magnitude in the microzooplankton biomass (from 2.4 mgC
m
2
to 380 mgC m
2
). The dominant dinoflagellates in winter were
Protoperidinium spp. (5.9 10
4
cells m
2
), Protoperidinium aff. sub-
inermis (5.7 10
4
cells cel m
2
), Dinophysis spp. (4.5 10
4
cel m
2
),
and Ceratium tripos (3.9 10
4
cel m
2
). In spring, the abundance was
almost entirely dominated by Diplopsalis spp. (6.810
6
cel m
2
)
followed by Protoperidinium steinii (4.17 10
5
cel m
2
)andC. tripos
(3.57 10
5
cel m
2
). At this station, microzooplankton removed HNF
atarateof1.5910
8
mgC ind
1
d
1
in spring and 1.24 10
7
mgC ind
1
d
1
in winter (Table 3A).
Copepod ingestion rates were similar in both seasons, with
2.7 10
3
and 2.8 10
3
mgC ind
1
d
1
in winter and spring,
respectively. The small copepod Paracalanus sp. was the most
abundant in both seasons, constituting 82% of the total
abundance. Less abundant species were Paracalanus spp., Calanus
spp., Acartia spp., and Rhyncalanus spp. The average ingestion
rates reported for Euphausia vallentini juveniles and adults in the
Comau Fjord (Sa
´nchez, 2007) were integrated for the upper 25 m
of the water column using only the euphausiid abundances
recorded in samples collected during night catches at St. 79 (due
to their pronounced vertical migration). Integrated euphausiid
ingestion rates ranged between 1.1 mgC m
2
d
1
in winter and
0.6 mgC m
2
d
1
in spring, mainly associated with the very low
euphausiid abundances during both periods.
Table 3
(A) Average individual grazing rates (mgC ind
1
d
1
), (B) average integrated (upper 25 m water column) abundance (no. ind m
2
), and (C) average primary production
(PP), vertical flux of particulates (VF), and grazing rates exerted by the integrated communities (mgC m
2
d
1
) of heterotrophic nanoflagellates (HNF), microzooplankton
(MICR), copepods, and euphausiids during the winter and spring cruises at the ‘‘process station’’ (St. 79).
Winter Spring
(A)
Grazing rate (mgC ind
1
d
1
) Grazing rate (mgC ind
1
d
1
)
HNF MICR Copepods Euphausiids HNF MICR Copepods Euphausiids
3.5 10
9a
1.24 10
7b
2.7 10
3c
0.05
d
5.6 10
10e
1.59 10
8f
2.84 10
3g
0.07
h
(B)
Integrated abundance (No. ind m
-2
) Integrated abundance (No. ind m
-2
)
HNF MICR Copepods Euphausiids HNF MICR Copepods Euphausiids
8.64 10
9
5.47 10
5i
168
j
21 1.69 10
10
1.1 10
7i
1159
j
8.8
(C)
PP (mgC m
2
d
1
) VF (mgC m
2
d
1
) Grazing rate (mgC m
2
d
1
)PP(mgCm
2
d
1
) VF (mgC m
2
d
1
) Grazing rate (mgC m
2
d
1
)
HNF MICR Copepods Euphausiids HNF MICR Copepods Euphausiids
8057615 n¼3 168 759 n¼15 30.2 0.1 0.5 1.1 831 7292 n¼3 266 770 n¼4 9.5 0.2 3.3 0.6
a
Range: 5.3–9.2 bact. HNF
-1
h
-1
(or 2.5–4.4 10
9
mgC ind
1
d
1
).
b
9.9 10
5
–1 10
4
m
gC ind
1
h
1
.
c
1.1.–3.1
m
gC ind
1
d
1
.
d
Average of E. vallentini juveniles and adults 51.8
m
gC ind
1
d
1
(Sa
´nchez, 2007).
e
1–1.3 bact. HNF
-1
h
-1
(or 4.7–6.3 10
10
mgC ind
1
d
1
).
f
3.6 10
6
–1.9 10 e
5
m
gC ind
1
d
1
.
g
1–7.7
m
gC ind
1
d
1
.
h
Average E. vallentini juveniles and adults 0.0667 mgC ind
1
d
1
(Sa
´nchez, 2007).
i
Tintinnids, thecate dinoflagellates 420
m
m, and copepod nauplii larvae.
j
Paracalanus spp., Calanus spp., and Acartia tonsa.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243238
The vertical carbon flux was nearly two times higher in spring
(266 mgC m
2
d
1
) than in winter (168 mgC m
2
d
1
)(Table 3C),
with zooplankton fecal pellets making the dominant contribution
to the vertical carbon flux.
4. Discussion
The spatial geomorphology of the study area includes
constriction sill structures that constitute physical barriers and
form three microbasins with distinct physical and biological
characteristics. These constrictions are the result of geological
glacial erosion and tectonic events (Borgel, 1970). The first
microbasin is defined by the presence of SAAW, loaded with
macronutrients, which flows from the Boca del Guafo passage
through Moraleda Channel (Silva and Guzma
´n, 2006) up to the
shallow (60 m depth) Meninea constriction sill. This water mass
mixes with freshwater coming from rivers and fjords, generating a
lower salinity water mass (31–33 psu) known as Modified
Subantarctic Water (MSAAW) (Silva and Guzma
´n, 2006). As the
MSAAW moves southward, it spills over the Meninea constriction
sill, filling the second microbasin, which extends up to the
Elefantes constriction sill. The third microbasin occupies a small
area between the Elefantes constriction sill and the last portion of
Moraleda Channel (close to the San Rafael Lagoon). This micro-
basin is filled with low-salinity water (o19 psu) from the
Northern Ice Field and the San Rafael Lagoon that is cold and
nutrient-depleted (NO
3
o7
m
M, PO
4
o0.8
m
M; Silva and Guz-
ma
´n, 2006). The physical (i.e., pycnocline depth) and chemical
(i.e., nutrient concentration) characteristics of the water that fill
these three microbasins and seasonal variability in solar radiation
may be the main factors affecting the magnitude and timing of
new production in the system. The spring and winter sampling
program was rather short (10 days per season) and was
conducted in an oceanographically variable area of the Chilean
Patagonia. Thus, on a seasonal scale, the conclusions should be
treated with caution because temporal limitations might occur.
However, the environmental conditions during the campaigns
(except for the time-series station 79) were as expected for both
seasons.
The chemical characteristics of the water masses in the study
area showed a conspicuous N–S gradient for certain parameters.
For example, high salinity values recorded at the Boca del Guafo
passage (33 psu) were progressively diluted by freshwater
towards the inner Moraleda Channel and up to Elefantes Gulf
(22 psu) (Fig. 4). The main rivers draining into Puyuhuapi Channel
and Aysen Fjord showed the highest discharges in the entire
Patagonian region (Cisnes River 178 and 288 m
3
s
1
and Ayse
´n
River 405 and 641 m
3
s
1
in summer and spring, respectively;
Calvete and Sobarzo, this issue), imposing dramatic changes on
the physical–chemical structure of the water masses and the
biological characteristics of the plankton structure.
High loads of Si(OH)
4
(20–47
m
M) are frequent in the low-
salinity surface waters of Puyuhuapi Channel (Silva et al., 1997),
whereas SAAW provides NO
3
(18
m
M) and PO
3
4
(2
m
M) below the
pycnocline. The MSAAW has lower levels of PO
3
4
and NO
3
than
the original SAAW (Silva and Guzma
´n, 2006), whereas the Si(OH)
4
concentration is expected to increase as salinity decreases due to
the input of freshwater high in silicic acid (11–167
m
M) from local
rivers (Silva and Guzma
´n, 2006). Nutrient concentrations are
lower in spring than in winter in the north microbasin (Fig. 4),
coinciding with this area’s high PP and Chl-avalues (Fig. 9) and
indicating active phytoplankton nutrient uptake. The dynamics of
Puyuhuapi Channel and Aysen Fjord seem to be different. These
areas receive high freshwater discharges from the Cisnes and
Ayse
´n rivers, with maximum flows in spring (Fig. 2), and probably
with a high particulate organic matter (POM) load that could be
exported in its dissolved form to the adjacent Moraleda Channel
and eventually to the oceanic region following the flow of the
estuarine water. However, the isotopic signal in the sediments
indicates significant enrichment in terrestrial POM only up to the
mouth of the fjords and channels in the area, in accordance with
the westward extension of the low-salinity surface water (Calvete
and Sobarzo, this issue; Silva et al., this issue). The surface silicic
acid:nitrate ratio ranges from o1 (Moraleda Channel: St. 102–39)
to 41 (Aysen Fjord) (Fig. 4) and suggests that waters deficient in
silicic acid and nitrate may be responsible for the magnitude of
the phytoplankton spring bloom. At the species level, distinctive
phytoplankton assemblages appeared in the microbasins: well-
silicified neritic diatoms such as Guinardia spp. were observed in
Moraleda Channel and lightly silicified diatoms such as Rhizoso-
lenia pungens and Leptocylindrus spp. were dominant in the fjords
(Fig. 9).
In spring, the north microbasin was dominated by high levels
of PP and Chl-a, which paralleled the elevated bacterial biomass
and POC. PP was favored by the intrusion of nutrient-rich SAAW
(Fig. 4), whereas mixing with the surface freshwater inputs (with
high silicic acid concentration) promoted the development of the
chain-forming diatom Guinardia spp. (Fig. 9). This species is an R-
strategist (ruderal) according to the Reynolds classification
(Reynolds, 1988), with a high surface:volume ratio, high efficiency
for harvesting light energy, and low efficiency for nutrient uptake
(Alves-de-Souza et al., 2008). This species dominated the
phytoplankton biomass up to the Meninea constriction sill and,
thus, the PP of the micro- and nanophytoplankton size-fractions
at St. 102 and 38. The high abundance of chain-forming diatoms
enhanced the production of phytoplanktonic polymeric exudates,
which supply DOC to promote bacterial biomass, allowing a close
coupling between phytoplankton, bacterial biomass, and the
enhanced production of POC. Overall, POC, Chl-a, and bacteria
biomass increased from two- to three-fold between winter and
spring (Fig. 5a). Bacterial biomass and Chl-aconcentrations
showed a significant positive correlation that increased from
winter (r
2
¼0.41) to spring (r
2
¼0.51), suggesting that photosyn-
thetic-derived DOM contributed a significant substrate for
heterotrophic bacterial utilization (Fig. 10). This might indicate
that algal-derived carbon is an important substrate for bacterial
growth in the Patagonian fjord area, even though allochthonous
0
Bacteria biomass (mg C m
-2
)
0
100
200
300
400
500
600
Spring
Winter y = 149.2+1.94*x
r
2
= 0.51
y = 97.1+2.92*x
r
2
= 0.41
Chl-a (m
g
m
-2
)
20 40 60 80 100 120 140 160 180
Fig. 10. Linear relationship between integrated (upper 25 m depth) bacterial
biomass (mgC m
–2
) and chlorophyll-aconcentrations (mg m
–2
) at all stations
sampled in winter (open dots) and spring (black dots) along Moraleda Channel,
Puyuhuapi Channel, Aysen Fjord, and Estero Quitralco.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 239
organic matter input is very important. A tight coupling between
phytoplankton production and bacterial utilization was found in
Puyuhuapi Channel where, over the course of one year (2007–
2008), the ratio between gross PP (495 gC m
2
y
1
) and micro-
bial, bacterial-based, community respiration (450 gC m
2
y
1
)
was close to one (Daneri et al., unpublished data). This suggests
that the reported high organic matter derived from allochthonous
sources (i.e. 24–85% in the Ayse
´n Fjord; Silva et al., this issue)is
required to subsidize the secondary production (i.e. heterotrophic
bacteria) in Patagonian fjord and channels as it is in several other
distinct environments such as rivers and lakes (Foreman et al.,
1998; Bukaveckas et al., 2002).
Bacterial biomass fluctuated moderately within a narrow
range in winter (100–200 mg m
2
) and spring (200–400 mg
m
2
), implying that bacterial mortality rates are in the same
range as bacterial production. Bacteria, in turn, are the main prey
of HNF, which are subsequently preyed on by both micro- and
small mesozooplankton (e.g., small copepods and larvaceans).
Thus, HNF act as a building block to sustain production in higher
trophic levels. In winter, the low bacterial biomass in the north
microbasin contrasted with high HNF (Fig. 5a), suggesting that the
bacterial biomass might be controlled by HNF bacterivory and
supporting the idea that bacterivory exerted by HNF constitutes
one of the major sources of bacterial mortality in aquatic
ecosystems (Fenchel, 1982; Sherr et al., 1992). In this sense, we
observed high ingestion rates (up to 9 bact. HNF
–1
h
–1
) by HNF in
winter (Table 3A), which resulted in heavy bacterial top–down
control (30.2 mgC m
2
d
1
;Table 3C) and which, indeed, was
supported by the lower bacterial abundance at that time (Fig. 5a).
On the other hand, in spring, HNF ingestion fell to 1 bact. HNF
–1
h
–1
,
with a subsequent lower grazing impact on bacterial communities
(9.5 mgC m
2
d
1
,Table 3C). Our estimations were within the
range of those previously reported in different studies, which
supported the feasibility of the size-fractionation method used.
For instance, Vargas et al. (2007) reported an ingestion rate of
25 bact. HNF
–1
h
–1
for a coastal area in central Chile using a
similar methodology. For another Chilean fjord ecosystem
(Reloncavı
´Fjord), Vargas et al. (2008) reported similar contrasting
feeding behavior, with ingestion rates from 13 to 19 bact. HNF
1
h
–1
in winter, dropping to 0.01–0.3 bact. HNF
–1
h
–1
in spring.
Furthermore, Czypionka et al. (this issue) used a different
methodological approach (uptake of fluorescent labeled bacteria,
FLB) to estimate the ingestion of both mixotrophic (MNF) and
heterotrophic (HNF) nanoflagellates in Ayse
´n Fjord during the
same field campaign of the present study. Those authors also
showed FLB ingestion by both MNF and HNF to be one order of
magnitude higher in winter. Bacterivorous flagellates usually
comprise a large number of taxonomically different forms, and
species-specific differences in feeding behavior might explain
seasonal variations in the grazing pressure by different HNF
communities (Boenigk and Arndt, 2000).
The increased production at higher trophic levels (mesozoo-
plankton) was visible in the form of a drastic increase of copepod
nauplii biomass in spring, which was especially evident at the
Boca del Guafo passage and the mouth of Moraleda Channel,
where SAAW dominated. Further south, Puyuhuapi Channel
seemed to play a pivotal role in modulating the phytoplankton,
bacterial biomass, and POC in the adjacent area of Moraleda
Channel. Blooms of chain-forming diatoms with high nutrient
requirements such as Rhizosolenia spp. (spring) and Thalassiosira
spp. (winter) were recorded in this channel (Fig. 9). High levels of
Chl-ain this channel were previously observed by Pizarro et al.
(2005) in spring and summer, and high, albeit variable PP rates
have also been measured and seem to be a frequent feature of this
channel; high levels of organic carbon (43%) were present in the
surface sediments (Silva and Prego, 2002). Unlike Puyuhuapi
Channel, Aysen Fjord usually displayed lower Chl-a, POC and
bacterial biomass, possibly related to the dilution of SAAW and its
modification to MSAAW (Silva et al., 1997), south of the Meninea
constriction sill. Because the Patagonian Puyuhuapi Channel and
Aysen Fjord lack glacial influences, they receive significantly
lower loads of inorganic fine sediment than do most fjords further
south (Pickard, 1971). The southernmost stations were mainly
dominated by low-salinity, oligotrophic waters (Silva et al., 1998)
that originated from the meltwaters of the San Rafael Glacier and
those associated with the Northern and Southern Ice Fields. The
high amounts of suspended silt that characterized this water
(Pickard, 1971) came from weathering processes that reduced
light penetration. Pizarro et al. (2005) observed that stations near
San Rafael Lagoon had the highest attenuation coefficients
(0.3–0.36 m
1
) and, therefore, the shallowest photic depth
(14 m depth), possibly limiting the local PP. Beyond the glacial
influence and adjacent to the ocean, the northern zone was found
to be free of cold waters and silt. Nutrient inputs from the ocean
(Silva and Neshyba, 1979) and light penetration to greater depths
(430 m) (Pizarro et al., 2005) favored PP in this area.
In winter, new production decreased sharply at all sampling
stations, whereas macronutrient concentrations seemed to be
non-limiting between seasons (Silva and Guzma
´n, 2006). Similar
observations were made by Gonza
´lez et al. (2010) in the northern
Patagonian fjords, where PP might be partially limited by solar
radiation due to the reduced photoperiod in austral winter.
Interestingly, the low PP reported for the pico- and nanophyto-
plankton size-fractions in winter for Elefantes Gulf, Puyuhuapi
Channel, and Aysen Fjord seemed to correspond to more
photosynthetically active organisms, as noted by the two- to
three-fold higher PP:Chl-aratios (vs. those reported for Moraleda
Channel). In spring, the situation reversed: PP:Chl-aratios were
high in the north microbasin (60), low in the south microbasin
along Moraleda Channel (30), and even lower in Puyuhuapi
Channel (5) and Aysen Fjord (20). This spatial variability in
phytoplankton activity might be related to the shift from a solar
radiation limitation control in winter to a nutrient limitation in
spring. In winter, the predominance of the pico- and nanophyto-
plankton size-fractions could be related to a better adaptation of
small-sized organisms (pico- and nanophytoplankton) to a low
light regime in the study area and low nutrient availability
(except silicic acid) in Elefantes Gulf, Puyuhuapi Channel, and
Aysen Fjord. Further studies need to address whether these
results might be related to the capacity of the picophytoeukar-
yotes to increase their Chl-asynthesis at lower light levels,
associated with photoacclimation processes, as seems to be the
case in transects conducted between the open ocean and the
Humboldt Current System off Chile (Grob et al., 2007).
Although the PP was similar in winter and spring at St. 79
(Figs. 9 and 11), the carbon export to the sediments was 58%
higher in spring than winter. Along the Chilean coast, the overall
fraction of PP exported below 100 m depth ranged from 1% to 60%
(Gonza
´lez et al., 2009). This high variability seems to have
biological origins, for example, differences in the quality and
quantity of the food-web structure and functioning at various
times and places (Legendre and Rivkin, 2002). The lower PP/Chl-a
ratio in spring (20) as compared to winter ( 70) (Fig. 9) could
be considered to be a proxy for a healthy (high values) vs.
unhealthy (low values) physiological condition of the phyto-
plankton. Along the Humboldt Current System off Chile, diatom
sedimentation was favored by large quantities of phytoplankton
with poor physiological conditions in the water column. This
factor alone was able to explain up to 49% of the variability in the
PP that sedimented as diatom frustules (Gonza
´lez et al., 2009).
Thus, during the spring campaign, the diatom carbon export was
four-fold higher, with lower physiological conditions than found
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243240
in the winter campaign, which may also partially explain the
higher carbon flux rate in spring despite similar PP in both
seasons. The expected positive relationship between PP and
carbon export was usually veiled by an enormous and highly
variable amount of freshwater loaded with particulate and
dissolved organic matter that entered the fjords and channels.
The total sedimented matter (seston) was composed mainly of the
lithogenic fraction (two-thirds of the seston remained after
combustion at 550 1C for 6 h). Zooplanktonic fecal material was
the most recognizable type of particle contributing to the POC
flux, and euphausiid fecal strings were the dominant type of fecal
pellet (46% of the total fecal material). Thus, the euphausiid
species of the genus Euphausia seem to be the key species
contributing large-sized, fast-sinking fecal strings to the carbon
flux in the northern Humboldt Current System (E. mucronata)
(Gonza
´lez et al., 2009), the north Patagonian fjords (E. vallentini)
(Gonza
´lez et al., 2010), and during this study, in the south
Patagonian fjords (St. 79 in the Ayse
´n Fjord).
At the time-series station (St. 79), the carbon flows through the
pelagic trophic food web in winter and spring (Fig. 11) were
conducted under typical winter environmental conditions (2–6
August 2007). However, unusual spring conditions (8–12 No-
vember 2007) with bad weather and cloudy days resembled a
typical winter period. Thus, these trophic flows can be considered
to be representative of the week of sampling but not the season.
We measured more integrated Chl-ain spring (average 42 mg
m
2
) than in winter (average 12 mg m
2
). The similar PP values
(800 mgC m
2
d
1
) resulted in higher PP/Chl-aratios for
winter, suggesting that the physiological condition of the
phytoplankton was healthier in winter. During both campaigns,
integrated bacterial biomasses were high and relatively constant
(200–300 mgC m
2
), indicating that the processes responsible for
heterotrophic bacterial growth and mortality rates were more or
less in balance. Higher biomasses of HNF and microzooplankton
were found in spring (74 and 236 mgC m
2
, respectively) than in
winter (28 and 3 mgC m
2
, respectively). In winter, the HNF
ingestion rate (bacterivory) was higher than in spring, whereas
the opposite was true for mesozooplankton, probably because
copepods and euphausiids were less abundant in spring but larger
in size than in winter (i.e., small cyclopoid and large calanoid
copepods dominated in winter and spring, respectively). The
vertical flux of particulates was slightly higher in spring than in
winter because of the higher contribution of particles such as fecal
pellets and aggregates of phytodetritus. For example, the fecal
material flux was almost two times higher in spring (16.9 mgC
m
2
d
1
) than in winter (10.3 mgC m
2
d
1
). In addition, the
particulate material collected in the sediment trap sample may
represent an integration of processes and events that largely
exceed in time and space the ca. two days of deployments and the
0.02 m
2
sediment trap collecting area.
In summary, topographic constriction sills partially modulated
the water exchange between the ocean (SAAW) and the fresh-
water river discharges along Moraleda Channel. The distribution
of newly formed MSAAW inside the fjords and channels could
affect their salinity, nutrient availability, and finally the plank-
tonic structure. In the north microbasin, the dominance of the
classical (spring) vs. the microbial (winter) food web seems to
follow the pattern described for the Inner Sea of Chiloe
´(Gonza
´lez
et al., 2010). Contrary to this, the south microbasin displayed
low productivity and a system dominated year-round by a large
input of glacier-derived, silt-rich freshwater and the dominance of
small-sized diatoms (i.e., Skeletonema spp.) and bacteria.
Puyuhuapi Channel and Aysen Fjord followed a different plank-
tonic dynamic in which the freshwater input (loaded with
allochthonous organic matter) exerted a more direct influence
on local productivity, food web dynamics, and vertical POC
exported to the sediments (two-fold higher in spring than winter).
Superimposed on this scenario was the highly seasonal variability
in solar radiation and photoperiod, which could exacerbate the
differences between the more productive north microbasin and
the less productive south microbasin.
Chl-a
12
Mesozoo
119
Microzoo
3
1
0
2
HNF
28
Bacteria
224
Fish
?
Vertical flux
168
PP 805
BSP
Winter
DOC
0.14
1.6
30.2
0.1
Chl-a
42
Mesozoo
60
Microzoo
236
1
0
2
HNF
74
Bacteria
307
Fish
?
Vertical flux
266
PP 831
BSP
Spring
DOC
0.17
9.5
0.2
3.9
Fig. 11. Integrated (upper 25 m water column) carbon biomasses (within circles,
in mgC m
–2
) and carbon fluxes (within arrows, in mgC m
–2
d
–1
) along the pelagic
food web. In addition, the primary production (PP) and carbon export towards the
sediments (vertical flux) are shown (dotted arrow and rectangle, in mgC m
–2
d
–1
).
Measurements were conducted in spring (upper panel) and winter (lower panel)
at the time-series station (St. 79) in Aysen Fjord.
H.E. Gonza
´lez et al. / Continental Shelf Research 31 (2011) 225–243 241
Acknowledgements
We would like to thank the captain and crew of the AGOR Vidal
Gormaz for their valuable support during the sampling program of
the CIMAR 13-Fiordos cruise. The dedication and highly professional
work of E. Menschel, F. Mun
˜oz, C. Carrasco, E. Teca, C. Torres, R.
Martı
´nez, P. Contreras, M.I. Mun
˜oz, and C. Valenzuela during the
in situ sampling and laboratory sample analyses are acknowledged.
We would also like to thank Susannah Buchan and Danielle Barriga
for the English editing.
Funding for this study was provided by the grants CONA-C13F
07-02 and CONA-C13F 07-07. Additional funds were received
from Fondap-COPAS 15010007 and the COPAS Sur-Austral PFB
31-2007 programs.
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... Such a current splitting would be expected to influence the biogeography of marine organisms, as it could potentially fragment the D. dianthus populations resulting in a clear genetic differentiation between northern and southern localities. The seasonal variability of the CHC 3,5 , and temporal variability in the phyto/zooplankton primary production 65,66 , as well as the seasonal reproduction of D. dianthus 67 support the absence of a genetic structure. The panmictic populations could enable long-term resilience to environmental and anthropogenic stress, and heavily-impacted populations could effectively be re-seeded by less-impacted populations. ...
... These conditions consequently affect the phytoplankton and zooplankton production, determining the areas as less productive than northern fjords 4,75 . Desmophyllum dianthus is a voracious predator, hence these conditions might limit the abundance of corals in southern channels 65,66,[76][77][78][79] . Another aspect is related to the environmental tolerance of the species: although D. dianthus is generally highly tolerant to environmental changes 80 , it does not seem to handle the combination of low pH and low O 2 concentration 81 . ...
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Comau Fjord is a stratified Chilean Patagonian Fjord characterized by a shallow brackish surface layer and a >400 m layer of aragonite-depleted subsurface waters. Despite the energetic burden of low aragonite saturation levels to calcification, Comau Fjord harbours dense populations of cold-water corals (CWC). While this paradox has been attributed to a rich supply of zooplankton, supporting abundance and biomass data are so far lacking. In this study, we investigated the seasonal and diel changes of the zooplankton community over the entire water column. We used a Nansen net (100 µm mesh) to take stratified vertical hauls between the surface and the bottom (0-50-100-200-300-400-450 m). Samples were scanned with a ZooScan, and abundance, biovolume and biomass were determined for 41 taxa identified on the web-based platform EcoTaxa 2.0. Zooplankton biomass was the highest in summer (209 g dry mass m ⁻² ) and the lowest in winter (61 g dry mass m ⁻² ). Abundance, however, peaked in spring, suggesting a close correspondence between reproduction and phytoplankton spring blooms (Chl a max. 50.86 mg m ⁻³ , 3 m depth). Overall, copepods were the most important group of the total zooplankton community, both in abundance (64–81%) and biovolume (20–70%) followed by mysids and chaetognaths (in terms of biovolume and biomass), and nauplii and Appendicularia (in terms of abundance). Throughout the year, diel changes in the vertical distribution of biomass were found with a daytime maximum in the 100–200 m depth layer and a nighttime maximum in surface waters (0–50 m), associated with the diel vertical migration of the calanoid copepod family Metridinidae. Diel differences in integrated zooplankton abundance, biovolume and biomass were probably due to a high zooplankton patchiness driven by biological processes ( e.g., diel vertical migration or predation avoidance), and oceanographic processes (estuarine circulation, tidal mixing or water column stratification). Those factors are considered to be the main drivers of the zooplankton vertical distribution in Comau Fjord.
Chapter
The export of newly produced organic carbon from the surface ocean and its regeneration at depth account for an estimated three-quarters of the vertical ΣCO2 gradient shown in Fig. 1 (Volk and Hoffert, 1985). If these processes, often referred to as the “biological pump,” had ceased operating during the pre-industrial era, the increase in surface ΣCO2 resulting from upward mixing of high ΣCO2 deep waters would have raised atmospheric pCO2 from 280 ppm to the order of 450 ppm (Sarmiento and Toggweiler, 1984) over a period of centuries. Vertical exchange, which gives an estimated upward flux of 100 GtC/yr (Fig. 2), works continuously to bring about just such a scenario. The biological pump prevents it by stripping out about 10 GtC/yr, so that the water arriving at the surface has a concentration equal to that which is already there.