Figure. Seasonally migrating copepods appeared at Station K2. We can identify two groups of the copepods by the life cycle.

Red: surface spawning species, Yellow: deep spawning species.

N. cristatus

N. plumchrusN. flemingeri

E. bungii

M. pacifica

C. pacificus

C. jashinovi

Day Night

Abundance (inds m-3)

Day Night

Day Night

CP

EB

MP

750-1000500-750400-500300-400200-300150-200100-150

50-1000-50

200 100 0

750-1000500-750400-500300-400200-300150-200100-150

50-1000-50

20 10 0

750-1000500-750400-500300-400200-300150-200100-150

50-1000-50

200 100 0

Depth distribution of surface-spawning copepods

Figure 4. Depth distribution of the surface-spawning species in the layers above 1000 m collected by IONESS. Abundance is mean of four day-night deployments during the study period (n=4). Bars show standard error.

Calanus pacificus concentrated their biomass above 50 m, and dominated by adult males and females. They w

ould emerge dormancy and start reproductions.

Eucalanus bungii showed two abundance peaks at surface and in mid-layers. Over the study period, they decreased younger specimens and they started a downwa

rd migration.

Metridia pacifica was a strong diel migrator, residing at mid-layers in daytime and at the surface in nighttime. T

hus, they are active.

De

pth

(m

)D

ep

th (

m)

De

pth

(m

)

Day Night

Abundance (inds m-3)

Day Night

Day Night

NC

NF

NP

750-1000500-750400-500300-400200-300150-200100-150

50-1000-50

30 15 0

750-1000500-750400-500300-400200-300150-200100-150

50-1000-50

10 5 0

750-1000500-750400-500300-400200-300150-200100-150

50-1000-50

300 150 0

Depth distribution of deep-spawning copepods

Figure 5. Depth distribution of the surface-spawning species in the layers above 1000 m collected by IONESS. Abundance is mean of four day-night deployments during the study period (n=4). Bars show standard error.

Younger specimens of Neocalanus cristatus appeared abundantly in the layers above 100 m and they were developing into overwintering stage toward the end of ou

r study period.

Overwintering stages were dominated Neocalanus flemingeri and they resided at the mesopelagic layers throu

ghout the study period, showing dormancy.

Neocalanus plumchrus was most predominant species among zooplankton community and concentrated over

wintering stage at the surface.

De

pth

(m

)D

ep

th (

m)

De

pth

(m

)

Table 1. Active carbon flux by the dominant diel migrants, Metridia pacifica and its comparison to POC flux. *Data from Ken.

Parameter 1 Aug. 5 Aug. 12 Aug. 16 Aug.

Migrant population

Abundance (102 animals m-2)

3.2 3.2 3.3 3.3

1.0 1.3 2.6 4.1

0.7 1.0 1.9 3.1

0.3 0.3 0.6 0.9

2.0 2.5 5.0 8.2

62.4 22.8

Weighted mean depth in daytime (m)

Ambient temperature in daytime (˚C)

Active carbon flux (mgC m-2 day-1)

Respiration

Egestion

- -

Biomass (mgC m-2) 56.8

10.5

215.5

60.1

31.9

243.5

110.5

82.4

214.9

189.0

107.3

185.9

Mortality

3.2 21.9 --

Total

POC flux (mgC m-2 day-1)*

Ratio of active carbon flux to POC flux (%)

Active carbon flux by Metridia pacifica is estimated to be 2-8 mgC m-2 day-1. Respiratory and egestion fluxes showed a similarly importance, and mortality flux was minor component.

These active carbon flux by the single species was accounted for more than 20% of sinking POC flux.

Comparing with the results of the world’s oceans, respiratory flux of K2 zooplankton community showed the largest numbers and was nearly equal to sedimentary flux in the NW Pacific as shown by Debbie.

Although Metridia pacifica was dominant diel migrants, they were accounted for 10% of the zooplankton respiratory flux.Therefore other zooplankton taxa would more important for respiratory flux.

Table 2. Respiratory flux (mgC m-2 day-1) by the diel vertical migrants in the world’s oceans modified from Al-Murairi & Landry (2001). ME: Mesozooplankton, MA: Macrozooplankton, MP: M. pacifica. PC: Particulate carbon flux.

Location Source

(mgC m-2) Component (%)

Atlantic

NFLUX 29 ME+MA 2 3 150 Longhurst et al. (1990)

BATS 192 ME 12 30 150 Dam et al. (1995)

BATS 49 ME+MA 1 5 Steinberg et al. (2000)

E. Equator 96 ME 3 15 150 Zang & Dam (1997)

Pacific

E. Equator 155 ME 6 20 150 Zang & Dam (1997)

E. Equator 53 ME+MA 6 4 150 Le Borgne & Rodier (1997)

W. Equator 47 ME+MA 3 6 Le Borgne & Rodier (1997)

ALOHA 158 ME+MA 4 15 Al-Murairi & Landry (2001)

Migrant biomass Flux Compared to PC

Depth (m)

150

150

150

ALOHA - ME+MA 1-5 7-29 Steinberg et al. (in prep.)150

K2 - ME+MA 10-29 16-127 Steinberg et al. (in prep.)150

K2 57-189 MP 1-4 2-3 Kobari et al. (in prep.)150

Table 4. Active carbon flux (mgC m-2 year-1) by the ontogenetic vertical migrants in the world’s oceans. CF: C. finmarchicus, NT: N. tonsus, NC: N. cristatus, NF: N. flemingeri, NP: N. plumchrus, Note: carbon flux at station K2 is shown as daily basis (mgC m-2 day-1).

Location Source

(mgC m-2) Spp. (%)

Atlantic Ocean

OWS I 346 CF 275 <1 200 Longhurst & Williams (1992)

ST - NT 3400 262 Bradford-Grieve et al. (2001)

STF

- NT 1700 340 1000 Bradford-Grieve et al. (2001)

Pacific Ocean

SAT

OWS P - NC+NF+NP 5000 185 1000 Bradford-Grieve et al. (2001)

Oyashio 7300 NC+NF+NP 4300 91 Kobari et al. (2003)

Migrant biomass Flux Compared to PC

Depth (m)

1000

Active carbon flux by ontogenetic migration of N. flemingeri was estimated to be 3 mgC m-2 day-1 and was accounted for 20% of sinking POC at 500 m.

Unfortunately, the active carbon flux by other two Neocalanus could not be estimated because they still resided at surface and were active.

If it depends on migrant biomass, other two Neocalanus species will produce much larger carbon flux than those by N. flemingeri.This flux could not be negligible and significant carbon pathway to the mesoplagic.

1000

K2 322 NF 3* 9-20 Kobari et al. (in prep.)500

Southern Ocean

- NT 9300 - Bradford-Grieve et al. (2001)-

K2 1757 NC+NP ? Kobari et al. (in prep.)- -

Picophytoplankton unedible for the copepods dominated primary production.We measured pigment concentrations in copepod guts and estimated feeding rate and its composition.

Phytoplankton composed <3% of the ingested carbon and their carbon demands should be relied on POC other than phytoplankton.Thus, their faecal pellets are also considered to come from non-phytoplankton materials.

These results suggest that some fraction of the exported carbon could be channeled through microbial food web and the copepod community.

Table 1. Community feeding rates and faecal pellets production by the ontogenetically migrating copepods in the layer above 150 m. *Data from Phil, **Data from Ken.

Parameter Source 1 Aug.

Units are mgC m-2 d-1, excepted for copepod biomass (mgC m-2) and ratio (%).

5 Aug. 12 Aug. 16 Aug.

Primary production (PP)* 590.1 427.5 300.3 355.2

Biomass 2427.1 1246.3 1267.3 1319.5

86.3 48.9 49.4 52.8

215.7 122.1 123.5 131.9

2.4 2.5 2.7 3.4

97.6 97.5 97.3 96.6

64.7 36.6 37.0 39.6

Respiratory requirement

Feeding rate

Ratio grazed

Faecal pellet production

Phytoplankton

Other POC

Ratio of PP Pico

Nano

Micro

48.2

17.7

34.1

47.8

22.8

29.4

56.8

21.7

21.5

59.9

22.5

17.6

Contribution of the copepod faecal pellets to sinking POC

Figure 6. Sinking POC flux and faecal pellet production (FPP) by the ontogenetic migrating copepods. POC flux at each layer was estimated from the formula of Pace et al. (1987) and primary production (Data from Phil).

Comparing with sinking POC flux estimated from the equation of Pace and others, the copepod community feces composed less than 10% of sinking POC above 150 m, and their contribution to sinking POC is considered to be small.

Since they were actively feeding on non-phytoplankton materials and transform them into faecal pellets, this process is considered to be an important carbon pathway during seasons dominated by small phytoplankton.

100-150

50-100

0-509%

3%

3%

10-1 101 102 103 104

7%

5%

4%

9%

6%

5%

10%

6%

5%

Flux (mgC m-2 day-1)

POC

FPP

1 Aug. 5 Aug. 12 Aug. 16 Aug.

What we knew from the ontogenetic migrants?

1. Most of the copepod community resided at surface during our study period and was developing with actively feeding on non-phytoplankton.

2. Carbon budget of the copepod feeding and egestion shows that a large fraction of their ingested carbon is channeled through microbial food web but their faecal pellets are minor component of sinking POC.

3. Active carbon flux by dominant diel migrant composed more than 20% of the sedimentary POC flux at 150 m and can be supplement source for the mesopelagic carbon demand.

4. Active carbon flux by ontogenetic migration of single species was account for 20% of the sedimentary POC flux at 500 m, and could be an important source for the mesopelagic carbon demand considering with the copepods residing at surface.