# Presentation: 281254

## Time-series station in the NW subarctic Pacific: ST. KNOT 44N, 155E, 1998-2000

- Time-series station in the NW subarctic Pacific: ST. KNOT 44N, 155E, 1998-2000

***Presenter: M.Chierici (NIES, Japan)***
***P.I: Yukihiro Nojiri (NIES, Japan)***
***N.Tsurushima, K.Imai, S. Watanabe others***

*Funded by CREST/*

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Planning of time series observation for Kyodo North pacific Ocean Time series

- <date/time>

**Planning of time series observation for ****K****yodo ****N****orth pacific ****O****cean ****T****ime series**

**JGOFS/North Pacific Task Team proposal**** for a new ocean time series station in the NW Subarctic Pacific (1996 Nov., Mutsu Symposium)**
**East/west comparison, subarctic/subtropical comparison with existing stations, P and HOT**

**Trial of**** time series occupations by R/Vs of opportunity**
**Cooperative (Kyodo) program within Japanese institutions**
**Funded by JST/CREST for 1998-2000 intensive survey period**

## #8

**Dense coverage from May to October, Less coverage from November to April**

- #10

- #9

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Slide 4

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## M/S Skaugran ship route of observation (Mar.1995-Mar.1999, 34 trips) and selected bands for seasonal functions. 

- 1 million of pCO2 data. Data north of 34N were served for analysis using pCO2 seasonal functions. Zeng et al., 2002
**M/S Alligator Hope from Dec 1999 to March 2001(16 trips), dense coverage in subarctic NP. ****Chierici et al. to be submitted**

- KNOT

- P

*WSG*

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## KNOT in the NW Subarctic Pacific has the largest seasonal amplitude in SST (HOT=3, P=7, KNOT=14 C).

**KNOT in the NW Subarctic Pacific has the largest seasonal amplitude in SST (****HOT=3****, ****P=7****, ****KNOT=14 ********C).**

- March

- September

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## SeaWiFS image for North Pacificsimilar surface chlorophyll with station P

**SeaWiFS image for North Pacific**similar surface chlorophyll with station P

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## New production map of North Pacific estimated from seasonal amplitude of nitrate in surface water observed by M/S Skaugran

**New production map of North Pacific estimated from seasonal amplitude of nitrate in surface water observed by M/S Skaugran**
- Contour is the seasonal amplitude of nitrate change in M.
- (Seasonal surface nutrient change) x (MLD) approximately proportional to new production.
- Summer MLD in Stn.P is almost twice as deep as MLD at KNOT;
-                                                             i.e.  similar new production for P and KNOT

- KNOT

- P

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Comparison of primary productivity between station KNOT and station P

**Comparison of primary productivity between station KNOT and station P**

- Imai *et al. *(2002)

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Zeng et al. (2002) pCO2 based on M/S Skaugran data (1995 to 1999)

- _KNOT area: _
- outgassing in winter
- Largest oversaturation in February (45)
- Early spring: sharp decrease in pCO2sw
- Summer and fall
- undersaturated by ~ 40 atm

- oversaturated

- undersaturated

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## halocline of 1 ppt

**Halocline at 100-200 m. Thermocline 100-120 m, depending on winter climate. Shallow summer thermocline (<20 m).**

**halocline of 1 ppt**

**Winter mixing depth**

- Summer MLD
-     < 20 m

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Surface DIC and Alkalinity (S=35 normalized)

**Surface DIC and Alkalinity (S=35 normalized)**
**Outliers are subtropical water intrusion.**

- 100mol/kg

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## SST time series

**SST time series**
**at Station KNOT**
**from 1998-2000**

- Interannual variability of SST

- Seasonal variability for each year

- No clear interannual variability in SST

- Seasonal SST amplitude ~ 14 C
- but no winter data

- Perhaps summer 1999 warmer than 1998

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Surface nitrate time series

**Surface nitrate time series**
**Outliers are subtropical water intrusion**

******NO3 >17**

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Observed seasonal change in surface fCO2 at KNOT 

**Observed seasonal change in surface fCO****2**** at KNOT **

*f*CO2sw ranged from 390 in May to 290 atm in Oct

- Two minima

- Tsurushima et al., 2002

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Using data obtained from VOS survey 2000 to take a look at KNOT area

- Example for fCO2sw, where t = time (month), c0 to c4 are seasonal terms
- fCO2sw (t) = c0 + c1 sin (2 t) + c2 cos (2 t) + c3 sin (4 t) + c4 cos (4 t)

- Lack of data in March and April at KNOT makes it difficult to address whether KNOT acts as an oceanic sink or source for atmospheric CO2.

- and what does
- the Grid data indicate....

- 100
- atm

- Chierici *et al., to* be submitted

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Sea-air CO2 fluxes at KNOT and from a 5Lon Grid 

- Wind speed from NCEP/NCAR Reanalysis
- monthly averages of 6-hr winds
- Flux parameterization: Wanninkhof, 1992

- _At KNOT:_ Oceanic sink of atm.CO2
- in summer and fall 7 to 10 mmol C m-2 d-1,
- Max. flux in Oct-99 of 14 mmol C m-2 d-1,

- Oct. flux agree

- Summer: KNOT sink

- However, using underway fCO2 data (VOS program) we estimated the sea-air flux in a larger area (5 Lon) and in the Western Subarctic Gyre (WSG), where KNOT is located in the SW corner
- (Chierici et al., to be submitted).
- Underway data indicates small oceanic sink of – 0.14 mol m-2 yr-1

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Modeled seasonal change in surface dissolved inorganic carbon in time series stations. DIC change of northern hemisphere station has a same phase but different amplitude.

**Modeled seasonal change in surface dissolved inorganic carbon in time series stations. ****DIC change of northern hemisphere station has a same phase but different amplitude.**

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Results of time series KNOT (1998-2000)

- 27 visits but uneven seasonal coverage
- Only MIRAI visit in true winter (2000)
- Absence of occupation in March and April, minimum SST period of vertical mixing
- Confirming maximum seasonal amplitudes in SST, nutrients and DIC in the time series stations
- Shallow mixed layer depth in the productive period
- Relatively small annual average PP (primary production), large seasonal amplitude in PP, and extremely low PP in winter

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## What learned from time series KNOT

- Difficulty in the open ocean time series
- 2-3 days of sailing to the time series location, minimum of two week cruise
- Ship time sharing with regular research cruise, unnecessarily long cruise for time series members
- Analytical quality control within different institutions, fortunately successful by standards and inter-calibration
- HOT and BATS time series
- Open ocean time series with neighboring island base, monthly visit by a fixed R/V of one week cruise
- Restart of KNOT time series occupation?
- Data set publication through JODC

- WG I: KNOT...Understanding NP C-cycle changes: workshop Seattle 2-4th June 2004

## Special thanks:

- <date/time>

**Special thanks:**
**KNOT core members**
**scientists of participating institutes and universities**
**participating research vessels**

**KNOT program is funded by JST/CREST.**

**KNOT data web site**
**(in preparation)**