Cascading of Dense Water along the Peter the Great Bay Slope in the northwestern Japan Sea

Transcription

1 PICES-2014 Annual Meeting, POC Papers, October 24, 2014, Yeosu, Korea Cascading of Dense Water along the Peter the Great Bay Slope in the northwestern Japan Sea V.Lobanov, A.Sergeev, I.Gorin, P.Scherbinin, A.Voronin, D.Kaplunenko, O.Popov, T.Gulenko and S.Ladychenko V.I.Il ichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia

2 Japan Sea geographic features Japan Sea - Deep semi isolated basin (>3500 m) - Inflow of Tsushima Warm Current from the south - Strong seasonal variations, ice formation - Winter monsoon winds bring cold dry air mass - Convective processes in the northern area control water mass properties - Deep convection and fast renewal of deep water

3 Japan Sea geographic features Japan Sea - Deep semi isolated basin (>3500 m) - Inflow of Tsushima Warm Current from the south - Strong seasonal variations, ice formation - Winter monsoon winds bring cold dry air mass - Convective processes in the northern area control water mass properties - Deep convection and fast renewal of deep water

4 Japan Sea geographic features Japan Sea - Deep semi isolated basin (>3500 m) - Inflow of Tsushima Warm Current from the south - Strong seasonal variations, ice formation - Winter monsoon winds bring cold dry air mass - Convective processes in the northern area control water mass properties - Deep convection and fast renewal of deep water

5 Winter convection processes Typical winter winds pattern (Kawamura et al., 1999) Brine rejection and slope convection Open sea convection Intermediate water ventilation m Oxygen min. layer Bottom water ventilation m Ventilation rates - turnover time: 300 yr - radiocarbon (Gamo and Horibe, 1983) 100 yr - tritium (Watanabe et al., 1991) yr -radium-226 (Harada and Tsunogai, 1986) 100 yr - radiocarbon (Kumamoto et.al, 1998) uncertainties indicate non permanent process of ventilation with large inter-annual variations (episodic events?)

6 Cascading in Peter the Great Bay - sea ice formation and brine rejection - fasten (stable) ice and drifting ice Cascading is a sinking of dense waters flowing from shelf seas down the continental slope. It occurs where dense water - formed by cooling, evaporation or ice-formation with brine rejection over the shallow continental shelf - spills over the shelf edge and descends the continental slope as a near-bottom gravity current. During its descent, the plume is modified by mixing and entrainment, and detaches off the slope when reaching its neutral buoyancy level. Observed at many slope locations of the world ocean (e.g. Shapiro and Hill, 1997; Shapiro et al., 2003; Ivanov et al., 2004; Canals et al., 2006; etc.) - contributes to ocean ventilation and water mass formation and hence ocean circulation; - vertical flux of chemical components; - transport of sediments, etc.

7 Cascading at PGB - previous studies 175 м Zuenko, 1998; 2000

8 Evidence of Cascading in a severely cold winter of 2001 and Ventilation of Bottom Water Владивосток Tpot-0, C T Salinity, psu S 1000 R1 R1 R2 Depth. m February March R2 April-May Oxygen, µmol/kg DO SiO4, µmol/kg Si 1000 Depth, m /9 R Lobanov et al., 2002; Kim et al., 2002; Senjyu et al., 2002; Talley et al., 2003; Tsunogai et al., 2003

9 Winter air temperature in Vladivostok (mean January and mean Dec-Feb) DEC-FEB JAN Winters 2012 and 2013 the coldest winters over recent 12 years and second coldest January T over 35 years after 2001

10 Observations of cascading in PGB during cold winters , , , 84 15, 82 14, 54, , , 56, 80 67, , 57, СИП1 7, 58, , 59, , 60, , 61, , 62, 74 СИП2 45 2, 63, , 64, CTD surveys (SBE19, SBE911, RBR-XR); - Moorings with T, S, DO, Turb, Flu and current meters (SBE37, RBR-XR, S4, RDCP600)

11 Pre-conditions for cascading - If there is enough dense water forms on the Peter the Great Bay shelf? - Its distribution and propagation toward the slope > CTD surveys

12 T and S at the surface and bottom layer of Peter the Great Bay < -1,82 C 43.4 T surf T btm , , , 84 15, 82 14, 54, , < -1,88 C , , 58, , 58, , 59, 78 6, 59, , 60, , 61, , 62, > 34,42 %o Распределение температуры на горизонте 5м, рейс 46, 27 февраля - 16 марта 2010 г. S surf S btm , 51 13, , , , , , 58, , 56, , 60, , 58, 77 6, 59, , 61, , 60, , 61, , 62, , 63, , 64, , 62, 74 2, 63, , 64, , 59, , , 84 15, 82 8, 57, , 57, , 54, , 81 9, 56, , 8415, 82 14, 54, > 34,75 %o Распределение температуры у дна, рейс 46, 27 февраля - 16 марта 2010 г , 64, , 63, , 62, , 64, , 63, , 61, , 60, , 56, 80 8, 57, , , 57, , 84 15, 82 14, 54, , , , 81 9, 56, Распределение солености на горизонте 5м, рейс 46, 27 февраля - 16 марта 2010 г. Распределение солености у дна, рейс 46, 27 февраля - 16 марта 2010 г.

13 , 68 67, , 65 13, 65 14, 54, , , 56, 80 8, 57, 79 7, 58, 77 6, 59, 78 5, 60, 76 4, 61, 75 3, 62, 74 2, 63, 71 1, 64, 72 14, 54, , , 56, 80 8, 57, 79 7, 58, 77 6, 59, 78 5, 60, 76 4, 61, 75 3, 62, 74 2, 63, 71 1, 64, 72 55, 81 55, , 84 15, , 84 15, Т, S diagram, Feb-March T btm < -1,88 C ,0 C 33,9 %o 0,08 C 34,07 %o S btm Распределение температуры у дна, рейс 46, 27 февраля - 16 марта 2010 г > 34,75 %o ,4 C 34,0 %o 42.1 < -1,88 C Распределение солености у дна, рейс 46, 27 февраля - 16 марта 2010 г. PB > 34,78 %o AB BS UB

14 Spatial and temporal scales of cascading > mooring observations

15 Shelf edge moorings Moorings with T, S, DO, Turb, Flu and current meters (SBE37, RBR-XR, S4, Infinity EM, RDCP600, WHS300)

16 Slope Convection in winter 2012 mooring period Feb 10 Apr ,5 T a) 34,4 34,3 34,2 b) S 0 34,1-0, ,9 33,8-1,5 33, , Turb c) 7 6 d) Chl-a , Variability of water temperature (a), salinity (b), turbidity (c) and chlorophyll-a concentration (d) in the bottom layer at the shelf edge of Peter the Great Bay in the period February 10 April 17, 2012.

17 1 0,5 0-0,5 34-0,8 C 33, ,4 C -1,5 Slope Convection in winter 2012 mooring period Feb 10 Apr days 4 days T a) 34,4 34,3 34,2 34,1 34,00 33,8 33,7 b) S , Turb c) d) Chl-a , Sigma theta > Feb 19-Mar 10 and Mar Variability of water temperature (a), salinity (b), turbidity (c) and chlorophyll-a concentration (d) in the bottom layer at the shelf edge of Peter the Great Bay in the period February 10 April 17, 2012.

18 Deep penetration of cascading water > 4 CTD surveys in 2012

19 CTD surveys Feb-Apr 2012 Feb Vladivostok Feb 28- Mar a) b) Mar Apr c) 42.2 d)

20 1 0,5 0-0,5 34-0,8 C 33, ,4 C -1,5 Slope Convection in winter 2012 mooring period Feb 10 Apr days 4 days T a) 34,4 34,3 34,2 34,1 34,00 33,8 33,7 b) S , Turb c) d) Chl-a , Sigma theta > Feb 19-Mar 10 and Mar CTD: Feb 08, Mar 01, Mar 15, Apr 17

21 Dense water approaches the shelf edge, 2012 Temperature Salinity Turbidity Chl-a Feb 08, Mar 01, Mar 15, Apr 17

22 Cascading along continental slope (Adapted from Fohrmann et al, 1998 and DeMadron et al., 2012) Cascading is a sinking of dense waters flowing from shelf seas down the continental slope. It occurs where dense water - formed by cooling, evaporation or ice-formation with brine rejection over the shallow continental shelf - spills over the shelf edge and descends the continental slope as a near-bottom gravity current. During its descent, the plume is modified by mixing and entrainment, and detaches off the slope when reaching its neutral buoyancy level. Observed at many slope locations of the world ocean (e.g. Shapiro and Hill, 1997; Shapiro et al., 2003; Ivanov et al., 2004; Canals et al., 2006; etc.) - contributes to ocean ventilation and water mass formation and hence ocean circulation; - vertical flux of chemical components; - transport of sediments, etc.

23 Cascading at Peter the Great Bay, 2012: February 8 T S DO Turb

24 Cascading at Peter the Great Bay, 2012: February 8 T S DO Turb - Intrusions of colder, less saline, higher in DO water around 550 m, 50 m thick

25 Cascading at Peter the Great Bay, 2012: March 1 T S DO Turb - Many intrusions down to 1200 m

26 Cascading at Peter the Great Bay, 2012: March 15 T S DO Turb - More intrusions down to 2200 m

27 Cascading at Peter the Great Bay, 2012: April 17 T S DO Turb - Less intrusions in upper layer, some intrusions below 1000 m

28 Deep penetration of cascading, 2012 All profiles over the slope during Feb-April 2012 Feb 08, Mar 01, Mar 15, Apr 17 T S DO - Intrusions of colder, fresher, higher in DO and turbidity water of m thick, - down to deep and bottom layers ( m)

29 What has happened then.? > Japan Basin CTD surveys in June 2012

30 T, S, DO profiles for deep Japan Basin, June 2012 T S DO no ventilation signal

31 Bottom Water Ventilation: Feb-Apr 2001 Tpot S T,S Feb-Mar 2001 Apr-Jun 2001

32 T, S, DO profiles for deep Japan Basin, June 2012 T S DO no ventilation signal

33 Different Ventilation Regimes Bottom waters Intermediate waters

34 Warming trend of bottom water temperature ( o C) in deep Japan Basin during ~0.002 C/yr Increasing trend of bottom water temperature ( m) in Japan Basin during associated with decreasing of ventilation. Deep ventilation event was observed in severely cold winter 2001.

35 Conclusion: - Peter the Great Bay shelf has good preconditions for dense water formation enough for cascading; - during cold winters of 2001 and 2012 a cascading of dense water down the slope was observed in Peter the Great Bay and probably it could happen in 2010 and 2011; - even in 2012 cascading was observed down to > 2500 m. However this injection of new water does not resulted in any noticeable changes of deep and bottom waters.

36 Thank you! -