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IARC Technical Report # 1

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7.3. Ice core sampling

7.3.1. Objectives (H.Eicken, GI)

The aim of the ice sampling is to complement the stable-isotope measurements carried out in the water column and to obtain additional data on the isotopic composition of the sea ice. This is of particular interest as the warming signal observed in the Laptev Sea is mostly associated with an influx of warmer AW (e.g., Polyakov et al., 2003). This water has a distinct isotopic signature (d18O approximately -0.3 °/°°) and one would hence expect to see a corresponding signature in sea ice that grew from water that contains a significant fraction of AW. This is illustrated in Figure 7.32 (shown below) which summarizes results from ice core measurements carried out in the Laptev Sea in 1993. Values in the lower parts of the ice core profiles that tend towards or above 0 °/°° are formed in water in the western Laptev Sea with substantial inflow and upwelling of AW. The interesting aspect here is that the ice cores actually record the growth history of the ice such that the ice formed in southern reaches of the Laptev Sea under the influence of riverine water is also identifiable.

7.3.2. Methods (H.Eicken, GI)

The field sampling and sample preparation program included the following steps:

(1) Ice coring: New ice that is only a few days or weeks old is of no interest to this study. Only older ice (first-year or second- or multiyear ice) was sampled at the stations where drifting buoys were deployed on the ice.

(2) Ice sampling: After drilling the cores, they were laid out on the ice and digital photographs were taken of the core. The total length of the core was measured. Then, samples for stable isotope measurements were cut from the core. It has been done immediately after sampling on the ice. The samples were cut with a simple handsaw.

(3) Sample bottling etc.: Samples were cut across the entire core cross-section. These core slices were 5 cm thick. In the upper half of the core they were cut every 20 cm; in the lower half of the core they were cut every 10 cm. These samples were transferred to plastic zip-lock bags, melted on the ship and then poured into small glass containers. Before pouring the water into the vials, the water was thoroughly mixed.


 


Figure 7.32: d18O measurements for three ice cores obtained in the Laptev Sea in 1993. The higher values in the lower ice layers indicate growth in water with significant fractions of AW.


 


Figure 7.33: Vertical distribution of salinity (psu, left panel) and temperature (°C, right panel) along the ice cores.

7.3.3. Preliminary Results (A.Klein, O.Andreev, AARI)

The ice core sampling was carried out on four ice stations (see Table 7.1 and Appendix 1 for details). The results of temperature and salinity measurements along the ice cores are presented on Figure 7.33. An example of the ice core with sampling cross-sections from the station ICE0403 is shown in Figure 7.34.

Figure 7.34: Ice core from the station ICE0403 with sampling cross-sections.

7.4. Biological Observations (M. Ringuette, LU)

7.4.1. Objectives

1. Comparison of state variables between the Laptev Sea and the Mackenzie shelf:

(The comparison of the spatial distribution of the mesozooplankton community and its biomass variability along and across the shelf brake area can be a serious test of the broad assumption that all the shelves are analogous throughout the entire Arctic ocean. This can also be an interesting complement to the work done during previous studies of the Laptev Sea [Kosobokova et al. 1998; Abramova 1999; Kosobokova and Hirche, 2001]

(Comparison of individual body length, biomass and state of maturity among the major common taxa;

(Without a sampling device able to stratify the water column, it is difficult to comply with the principal aim of the NABOS program which is to study the intrusion of AW masses into the Arctic Ocean. However, the "Sea Mount Feature" can represent an oasis of heat and food [Dower and Mackas, 1996; Dower and Perry, 2001] and maybe also a retention zone [Flint and Yakushev, 1988] for larval fish. We will insure that this feature is well sampled.

2. Determination of the vertical distribution of small species of zooplankton:

The calibration with the rosette will provide an easier and more accurate way to measure spatial and vertical distribution of the small size fraction of the mesozooplankton. The problem with conventional methods of collection is the large quantity of phytoplankton. The small copepods tend to agglomerate within the phytoplankton, making it almost impossible to fractionate the sample for counting. The small volume of water sample harvested with the CTD-Rosette is about the same as the sample volume we actually require, relieving us of the necessity of further subdividing the samples [Nielsen and Andersen, 2002].

3. Growth rate comparison of Boreogadus Saida amongst different polynyas including the Laptev and the Bathurst polynya (Mackenzie area, CAN):

The Arctic cod represent a funnel, through which the carbon cycle must pass in order to sustain the high biomass of the higher trophic levels (birds, seals and polar bears) [Welch et  al., 1992]. Apart from the very first weeks of life, we know little about the life cycle of this important species. It is believed that the adult cod use the disturbed pack ice as a habitat, and several observations tend to corroborate that belief. In summer the cod aggregate in large schools whose biomass can attain several tons [Welch et al., 1992]. The rest of the life cycle is poorly described, including reproductive activities and egg development in the natural environment. By comparing different habitats and ecosystems we aim to distinguish between local factors that can promote growth and survival, and general species adaptation to the cold Arctic environment. Study of genetic differentiation in different fish stocks across the Arctic holds potential for defining the structure of the whole arctic population.

7.4.2. Methods

The sampling area is shown in Figure 7.35. A conical net of 1 m diameter and 200µm mesh equipped with a TSK flowmeter was towed to every station from 500 m to the surface, or from the bottom when the water was shallower than 500 m. On the side, a small net of 10 cm in diameter with 50µm mesh was installed to allow the capture of the smaller species of interest along with the young nauplii stages. This setup allows us to uniformly sample the water column where all the target species are living and to preserve them in 4% buffered formalin solution. Samples will be analyzed to identify the lowest taxonomic level in the coming fall at Laval University.

We sorted individual copepod species which dominate the Arctic Ocean (Calanus hyperboreus, C. glacialis and Metridia longa), placed them into a pre-weighted boat, and will maintain them in desiccant until our return to the lab in Québec where they will be re-weighed. Those individual measurements will be used for comparison between the two regions. Along with this, we will measure a reproductive index (RI), following Niehoff [1998], allowing us to compare the reproductive state of the two populations. The vertical distribution of the small copepods will be assessed by comparing the results from using the CTD-Rosette system with the results obtained using the small 50µm net.

Juvenile Arctic cod were caught with the double Tucker-like trawl. This trawl consists of two 1m2 nets installed side by side on a rectangular frame and equipped with a flowmeter. Juveniles caught were individually measured fresh and preserved in 95% ethanol. Otoliths will be removed in the lab, and will be used to estimate individual daily growth. Stomach contents will also be analyzed.

7.4.3. Preliminary Results

Mesozooplankton

Data from the sorting stations indicate that Calanus finmarchicus, a typical north Atlantic species, seems to be present at every station north of the shelf break area. On the other hand, this species is at the very end of its latitudinal distribution. The very low temperature that prevails in the Arctic region throughout the whole summer enables C, finmarchicus to successfully reproduce. The amphipod Themisto libellula was very abundant throughout the entire sampling area and clearly dominates the large size fraction at the least shallow stations. The population was composed of at least three different cohorts, or year classes.

We aim to measured density, total biomass of the mesozooplankton community, and individual dry weight back at the Québec Lab. Individual dry weights were taken from stations at each extremity of the sampling grid.

Figure 7.35: NABOS2003 biological sampling map.

In addition a trial experiment was done in order to measure individual faecal pellet production. Thirty-two live female adult animals of different species (8 C. hyperboreus, 8 C. glacialis, 8 C. finmarchicus and 8 M. longa) were incubated individually in scintillation vials filled with 50µm filtered sea water. Incubation temperature was maintained around 0°C throughout the 24 hours of the experiment. Pellet production will be measured later on in the lab. The variation in species and stage will then allow us to explore the morphology and quantification of faecal pellet carbon content for future work with long and short sediment traps.

Vertical distribution of small organisms and calibration

A total of eight stations were sampled at six different depth strata (Table 7.8). Again, all the taxonomical work will be done in the Laval University Lab.

Table 7.8: Sampling of the small zooplankton using the CTD-Rosette system.

Station

Date

Time (GMT)

Latitude (N)

Longitude (E)

Depth Strata (m)

KD1303

5/09/03

06:12

79°00.3'

144°00.5'

0, 10, 15, 25, 50, 75, 86

KD1403

5/09/03

12:24

79°29.2'

140°41.3'

0, 25, 50, 75, 100, 300

KD1603

6/09/03

08:32

79°14.3'

132°20.5'

0, 25, 50, 75, 100, 300

KD2003

09/09/03

10:22

77°44.5'

125°59.3'

0, 25, 75, 150, 300

KD2103

09/09/03

15:15

77°30.2'

126°00.8'

0, 25, 50, 75, 100, 300

KD2303

10/09/03

00:50

77°15.2'

126°02.7'

0, 25, 50, 75, 100, 300

KD2503

11/09/03

02:23

77°00.5'

126°04.3'

0, 25, 50, 75, 100, 300

KD2603

11/09/03

05:25

76°44.8'

126°00.4'

0, 10, 15, 25, 40, 50

Juvenile Arctic cod

We were able to sample for fish where ice conditions allowed it, at thirteen different stations during this cruise, mostly in the southern parts of the transect (see Table 7.9). Among the 153 fish captured, 150 were Arctic cod (Boreogadus saida) and three belong to other species. One of these three remains unidentified, and will require more work with the taxonomy literature. The other two are from the family Cottidae.

For a subset of 50 juveniles, the mean standard length is 29.81 mm. The bimodal distribution suggests a population with two cohorts belonging to two different hatching events, separate in time and/or in space. According to the age-length key from the North Water polynya in 1999, a difference of 10mm in mean length corresponds to a difference of 30 days in growth. This relationship will need to be confirmed by measurements of individual growth.


Figure 7.36: Standard length distribution of the Arctic cod, Boreogadus saida in the September 2003 in the Laptev Sea.

Table 7.9: List of stations sampled with the horizontal net and number of juvenile fish catches.

Station

Date

Time (GMT)

Latitude (N)

Longitude (E)

# of

Arctic cod

# of other

KD0603

03/09/03

11:20

79°49.7

133°27.9'

1

0

KD1103

05/09/03

1:02

79°24.1'

143°03.9'

0

0

KD1203

05/09/03

4:02

79°15.9'

143°30.9'

0

0

KD1303

05/09/03

6:57

79°00.8'

144°02.6'

0

0

KD1603

06/09/03

8:07

79°14.7'

132°22.1'

0

0

KD1903

09/09/03

6:13

78°05.2'

126°19.5'

0

0

KD2003

09/09/03

12:34

77°41.7'

125°57.9'

0

0

KD2103

09/09/03

17:13

77°29.6'

126°06.1'

0

0

KD2203

09/09/03

22:04

77°14.6'

127°23.5'

0

0

Station

Date

Time (GMT)

Latitude (N)

Longitude (E)

# of

Arctic cod

# of other

KD2303

10/09/03

3:05

77°15.0'

126°08.2'

0

1

KD2403

11/09/03

00:01

77°14.5'

124°50.7'

0

0

KD2503

11/09/03

3:22

77°00.5'

126°06.9'

7

0

KD2603

11/09/03

6:15

76°44.7'

126°00.0'

146

3

       

Total

154

4

 

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