ALPHA HELIX CRUISE HX260

Thursday 20th June 2002- Saturday 29th June 2002

BERING STRAIT CRUISE REPORT

 

FUNDING SOURCE:     NSF-OPP-0125082 (Grebmeier, U of TN)

 

CHIEF SCIENTIST:       Rebecca Woodgate

                                         University of Washington, Applied Physics Laboratory

                                         1013 NE 40th Street, Seattle, WA 98105-6698.

                                         Phone:    206-221-3268

                                         Fax:        206-616-3142

                                         Email:   woodgate@apl.washington.edu

 

SCIENTIFIC PERSONNEL:

   Rebecca Woodgate                       APL, Moorings                            (F, Chief Scientist)

   Roger Andersen                             APL, Moorings                            (M)

   Terry Whitledge                              UAF, Nutrients & Sampler         (M)

   Sarah Thornton                              UAF, Nutrients & Sampler         (F)

   Sang Heon Lee                               UAF, Nutrients & Sampler         (M)

   Clara Deal                                      UAF, DMS sampling                  (F)

 

SCIENTIFIC PURPOSE:

This cruise had two main scientific goals. 

The first (and foremost) was the recovery and redeployment of moorings in the Bering Strait.  These moorings are part of a multi-year time-series (currently over 10 years long) of measurements of the flow through the Bering Strait.  The properties of this flow not only influence the Chukchi and Beaufort Seas, but can also be traced across the Arctic to the Fram Strait and beyond.  The long-term monitoring of the inflow into the Arctic Ocean via the Bering Strait is important for understanding climatic change both locally and in the Arctic. 

Three moorings (A2 and A4, in the eastern channel of Bering Strait, and A3, c.35nm north of Bering Strait), which were deployed from the Alpha Helix last year, were  recovered and redeployed.  All the moorings carry conventional instrumentation - current meters (RCM), temperature and salinity sensors (SBE16).   In addition, moorings A2 and A3 carry Upward-Looking-Sonars (ULS).  The new mooring A4 carries an upward-looking ADCP to study the coastal jet.  Mooring A3 also supports a nutrient sampler from UAF, and the replacement mooring carries in addition a transmissometer, a fluorometer and a PAR sensor, all connected to the SBE16.  The current meters and ULSes allow the quantification of the movement of ice and water through the strait.  The nutrient sampler and the optical sensors should yield the first biophysical time series measurements in the region, greatly advancing our understanding of the biological system in the Bering Strait and Chukchi Sea.

The second aim of the cruise was to conduct a hydrographic and ADCP survey of the Bering Strait and the southern part of the Chukchi Sea, concentrating on sections in the vicinity of the moorings and the region north of the mooring sites.  These CTD and nutrient measurements will be used to calibrate the moored instruments and to give a framework for the analysis of the data.  The hydrographic lines repeated and extended the surveys from previous years, allowing an interannual comparison.  

Our application to work in the Russian EEZ, submitted in December 2001, was turned down in June 2002.  Thus, all section and mooring work was confined to the US EEZ or international waters.

In addition to maintaining the time series measurements in Bering Strait, this work will also act as a upstream boundary condition for the NSF SBI (Shelf Basin Interaction) program, which starts its field work sampling this year.

 

CRUISE OBJECTIVES:

1.  To recover moorings A2-01, A3-01 and A4-01 (see Table 1).

2. To deploy moorings A2-02, A3-02 and A4-02.  As time/weather permits, to run hydrographic casts (CTD and nutrients) and ADCP sections in the vicinity of the moorings and in the southern region of the Chukchi Sea (see Table 2 and Figure 1).

 

Due to exceptionally good weather, all the cruise objectives were successfully accomplished.  The moorings were recovered and redeployed, and a total of 98 CTD stations, and corresponding ADCP lines were run.  Sampling details are provided below.

 

CRUISE SCHEDULE:

(Times are generally to the nearest half hour, and are in AKDS time, i.e. GMT-8hrs.  The map in Figure 1 gives the location of the CTD and ADCP lines.)

20th June 2002                 Join Alpha Helix at 9am, sail from Dutch Harbor at 1125

21st June 2002                 Transit to Bering Strait

                                         0705 Primary productivity station at site M2

22nd June 2002                Transit to Bering Strait

23rd June 2002                 Arrive Bering Strait at 1410

                                         1410 Primary Productivity Station at site A2

                                         1530-2100 CTD section along BS line

                                         2100-2400 ADCP section along BS line

24th June 2002                 0100-0400 ADCP section along MBS line

                                         0400-0830 CTD section along MBS line

                                         0900-1100 Recover and redeploy A4

                                         1200-1330 Recover and redeploy A2

                                         1730-1930 Recover and redeploy A3

                                         1930-0230 CTD section along A3L line

25th June 2002                 0230-1000 ADCP line along A3L line

                                         0947 Primary Productivity Station at site A3

                                         1500-0530 CTD and ADCP along PHL line

26th June 2002                 0530-1130 ADCP out to CCL line

                                         1130-2400 CTD section along CCL line, including

                                         1656 Primary Productivity Station at CCL15

27th June 2002                 0000-1000 ADCP section along CHUK and EEXT lines

                                         1000-2030 CTD section along EEXT and CHUK lines

                                         2030-0230 CTD section along CCL line (continued)

28th June 2002                 0230-0900 ADCP section along NBS line

                                         0900-1700 CTD section along NBS line

                                         1700-1930 CTD section along CCL line (continued)

                                         1930 Close of science, steam for Nome

29th June 2002                 arrive Nome ca.0700 and disembark

 

SAMPLING:

 

Due to the exceptionally good weather we encountered, we were able to complete the mooring work and an extended CTD and ADCP plan. 

 

Mooring Work:

All three moorings (see Table 1) were successfully and smoothly recovered and redeployed.  Releases functioned well.  All instrumentation was recovered in good condition.  Unlike in previous years (when mooring recoveries took place in the autumn), the moorings were not badly fouled and the rotors and salinity cells were reasonably clear of biological growth.

Of the three RCMs, two gave good data.  The third (A2) developed a battery short before deployment and recorded no data.  The three SBEs appear to have run well.  The ULSes were still working on recovery and binary data was successfully downloaded.  Although both records were complete, one ULS (A2) did not record any echo returns after January.  The nutrient analyzer ran for ca. 1 month before a mechanical plunger jammed.  (The unused chemicals from the analyzer were still in good condition after a year in the water.)

 

CTD and ADCP section work:

See Figure 1 and Table 2 for the CTD and ADCP sections ran.  A total of 98 CTD casts were taken.  (Three profiles were recast since the CTD acquisition software crashed part-way through the up-cast.)  Preliminary section plots are given in an Appendix.  Bottles were fired at standard depths (bottom, bottom-2m, 50m, 40m, 30m, 20m, 10m, 5m, surface) and samples were taken for nutrients, DMS, chlorophyll, O18 isotopes, nitrogen isotopes and salinity.  With the exception of the PHL and CCL lines, ADCP sections were run as dedicated sections at a speed of 7 knots.

 

Nutrient Analysis work (Whitledge, Thornton, Lee):

A total of 536 nutrient samples were taken and analyzed on board for silicate, phosphate, nitrate, nitrite and ammonia by Whitledge, Thornton and Lee.  Preliminary section plots are included as an appendix.  In addition, at many stations samples were taken at surface, mid water column and bottom for chlorophyll, and at some stations samples were taken for size-fractionated chlorophyll, fractionated on 20um, 5um and GF/F filters.  At the four sites M2, A2, A3 and CCL15, primary productivity stations (stable isotope nutrient enrichment primary productivity experiments with 15N-labeled nitrate and ammonia and 13C-labeled carbon) were also run.

 

DMS Analysis work (Deal):

DMS sea water profiles were taken at 18 stations, namely

June 23: A2-P

June 24: A4, A2, A3

June 25: PHL1, PHL6, PHL11

June 26: CCL12

June 27: EEXT3, CHUK10, CHUK7, CHUK2, CCL08

June 28: A3, NBS11, NBS7, NBS2, NBS1.

These samples were analyzed on board by Deal.

 

Oxygen isotope sampling (Woodgate for Cooper, Tennessee):

A total of 379 water samples were taken for O18 sampling.  Samples were taken at all stations except some of the productivity stations (see bottle list in an appendix).  These samples were sealed with parafilm and shipped to Lee Cooper at the University of Tennessee for later analysis.  To ensure the integrity of the bottle samples, when possible salinity samples (ca. 200) were taken from the bottles used for O18 samples.

 

Nitrogen Isotope sampling (by Deal for Tanaka, IARC/UAF)

Nine water samples (3 each at sites A2, A3 and A4) were taken for nitrogen isotope analysis.  These samples will be analysed post cruise by Dr Tomoyuki Tanaka, IARC/UAF. 

 

Underway sampling:

Seachest data showed evidence of some remarkable fronts during transit and in the work area.  For example, passing St Lawrence Island in the early evening, we encountered a few remaining small pieces of ice and a remarkably strong front in surface temperature and salinity.

The flow through Bering Strait was generally towards the south, reflecting the southward winds.  For the first few days in Bering Strait, the coastal jet was not easily identifiable (though a more comprehensive check of the ADCP data is required to confirm this).  For the latter part of the cruise, although the general flow was still southward, there did appear to be some evidence of the boundary current.

 

 

FIGURE 1: Overview Map of the Work Area

 

 


 

TABLE 1: Mooring Positions and Instrumentation

 

 

ID

LATITUDE (N)

LONGITUDE (W)

WATER DEPTH /m

INST.

 

 

 

 

 

Recovered

 

 

 

 

A2-01

65° 46.76'

168° 34.52'

56

ULS

 

 

 

 

RCM7

 

 

 

 

SBE16

 

 

 

 

 

A3-01

66° 19.58'

168° 58.03'

57

ULS

 

 

 

 

RCM9

 

 

 

 

SBE16

 

 

 

 

NAS-2E

 

 

 

 

 

A4-01

65° 44.73'

168° 15.83'

48

RCM7

 

 

 

 

SBE16

 

 

 

 

 

 

 

 

 

 

Deployed

 

 

 

 

A2-02

65° 46.77'

168° 34.53'

56

ULS

 

 

 

 

RCM7

 

 

 

 

SBE16

 

 

 

 

 

A3-02

66° 19.56'

168° 58.03'

57

ULS

 

 

 

 

RCM11

 

 

 

 

SBE+TF

 

 

 

 

NAS-2E

 

 

 

 

 

A4-02

65° 44.70'

168° 15.78'

49

ADCP

 

 

 

 

SBE16

 

 

 

ULS = APL Upward Looking Sonar

RCM7 = Aanderaa Mechanical Recording Current Meter

RCM9 = Aanderaa Acoustic Recording Current Meter

SBE16 = Seabird CTD recorder

SBE+TF = Seabird CTD recorder with transmissometer, fluorometer and PAR sensor

NAS-2 = Nutrient Analyzer

ADCP = RDI Acoustic Doppler Current Profiler

TABLE 2: CTD Positions

 

Name           #     Time (GMT)         Stat         Lat(N)      Long(W)     D    P-   P+

hx2600001   1  Jun 21 2002 15:05  m2           57  5.83   165  5.22     72  3.1 69.8

hx2600002   2  Jun 23 2002 22:13  a2p          65 45.80  168 34.09     57  2.2 52.2

hx2600003   3  Jun 23 2002 23:42  bsl6         65 40.93  168 10.89     26  1.6 28.3

hx2600004   4  Jun 24 2002 00:17  bsl5         65 41.37  168 15.22     42  2.0 45.1

hx2600005   5  Jun 24 2002 00:46  bsl5         65 41.78  168 19.52     51  2.5 53.7

hx2600006   6  Jun 24 2002 01:23  bsl4.5      65 42.15  168 24.01     54  1.1 51.3

hx2600007   7  Jun 24 2002 01:49  bsl4         65 42.62  168 28.20     51  2.2 52.5

hx2600008   8  Jun 24 2002 02:18  bsl3.5      65 43.05  168 32.38     54  1.9 54.8

hx2600009   9  Jun 24 2002 02:46  bsl3         65 43.50  168 36.98     54  1.4 51.0

hx2600010  10  Jun 24 2002 03:22  bsl2.5     65 43.72  168 40.86     50  1.7 51.4

hx2600011  11  Jun 24 2002 03:46  bsl2        65 44.12  168 45.04     50  2.2 52.8

hx2600012  12  Jun 24 2002 04:19  bsl1.5     65 44.75  168 48.65     50  1.9 52.6

hx2600013  13  Jun 24 2002 04:45  bsl1        65 45.49  168 52.12     40  2.2 42.6

hx2600014  14  Jun 24 2002 12:03  mbs1      65 52.09  168 57.04     43  2.0 41.8

hx2600015  15  Jun 24 2002 12:40  mbs2      65 51.88  168 49.05     50  2.1 50.3

hx2600016  16  Jun 24 2002 13:14  mbs3      65 51.69  168 40.94     51  2.1 51.4

hx2600017  17  Jun 24 2002 13:48  mbs4      65 51.55  168 31.92     55  1.9 51.8

hx2600019  19  Jun 24 2002 14:37  mbs5      65 51.37  168 23.01     50  2.2 51.3

hx2600020  20  Jun 24 2002 15:13  mbs6      65 51.13  168 13.92     50  2.3 46.7

hx2600021  21  Jun 24 2002 15:45  mbs7      65 50.96  168  6.93      40  2.3 38.5

hx2600022  22  Jun 24 2002 16:05  mbs8      65 50.93  168  5.04      32  2.6 30.7

hx2600023  23  Jun 24 2002 17:44  a4-01      65 44.68  168 15.94     45  2.1 46.5

hx2600024  24  Jun 24 2002 20:49  a4           65 46.74  168 34.36     54  2.1 53.8

hx2600025  25  Jun 25 2002 02:18  a3           66 19.58  168 58.18     54  2.5 53.4

hx2600026  26  Jun 25 2002 04:14  A3L2       66 21.26  168 48.38     57  2.5 53.6

hx2600027  27