Title
Low sea surface salinity in the Japan Sea during the last glacial maximum

Members’ names and affiliations
NameKailun Du
Huiwang Gao
Jie Shi

Institution andDepartment
Ocean Universityof China
Ocean Universityof China
Ocean

Employment position
Masterstudent
Professor

courseUniversity Associate Professorof China
Xinyu Guo

Faculty member of Professor
LaMer

Aim
This project aims to clarify the sea surface salinity in the Japan Sea during the last glacialmaximum (LGM) and to estimate the impacts of the volume transport through Tsushima Strait aswell as evaporation and precipitation on the reduction of sea surface salinity. It also aims to promote
cooperation and students exchange between the College of Environmental Science and Engineeringof Ocean University of China and the Center for Marine Environmental Studies (CEMS) of Ehime
University.

Procedure
The principal investigator (PI) made an oral presentation “Low sea surface salinity in the JapanSea during the last glacial maximum” and showed the recent studies including:1

The lower sea surface salinity in the Japan Sea is due to the evaporation and precipitationand the weakening of water exchange in the Tsushima Strait during the LGM.

2The annual mean precipitation exceeds evaporation and the fresh water input the JapanSea during the LGM.

3The reduction of volume transport through Tsushima Strait due to the decrease in sea levelplays a vital role in the change of sea surface salinity over the Japan Sea.

Results
1. The precipitation and evaporation simulated by PMIP3 models
We collect LGM simulations from the Paleoclimate Modelling Intercomparison Project, Phase
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3 (PMIP3) and compare these simulations to the experiments of Preindustrial (PI) and Mid-Holocene(MID). The annual mean precipitation and evaporation are given in Figure 1, simulated by thePMIP3 models. The LGM precipitation is slightly less than the PI and MID, and simultaneously, theevaporation also decreases compared with that in other periods, which is related to the reduction of
air temperature and weakening of solar radiation during the LGM. These indicate that the net
freshwater input in Japan Sea was mainly caused by the decrease of evaporation rather than by theincrease of precipitation in the LGM.

Fig. 1. The annual mean precipitation and evaporation for PI, MID and LGM, simulated by each of
the seven PMIP3 models (CCSM4, CNRM, FGOA, IPSL, MIROC, MPI, MRI).

Fig. 2. The seasonal variation of the precipitation minus evaporation for PI, MID and LGM,simulated by each of the seven PMIP3 models (CCSM4, CNRM, FGOA, IPSL, MIROC, MPI,MRI).
The seasonal variation of precipitation minus evaporation over the Japan Sea in the three
periods is very similar (Fig.2). In winter, the precipitation was less than the evaporation, and insummer, the precipitation was greater than the evaporation. During the PI and Mid-Holocene, theprecipitation exceeds the evaporation from April to August. The Japan Sea has fresh water input andthe value is 0.0005-0.05 SV (1 Sverdrup = 106 m3/s). The Japan Sea has also fresh water input from2 / 4

March to September (0.001-0.05 SV) in the LGM. Because the change of precipitation andevaporation is so uncertain, the precipitation minus evaporation value is given as the constant during
our calculation.
2 The salinity simulation
We use a simple ocean model (Fig.3) and attempt to simulate the paleoclimatic change of theJapan Sea in th last glacial maximum. In the present work, only the upper 200 m layar of the Japan
Sea is included in the model, and interactions with the lower are omitted. The volume of the upperlayer is fixed in the model, W = 1.5 ×1014 km3( Yanagi, 2002).The salinity of the Tsushima Strait ischosen to be Sd = 33±1.0 ‰(Matsui et al., 1998). The fresh water flux includes river discharge(0.0044 Sv) and precipitation minus evaporation.

dSt Vt  Sd -(Vt + R )  St=dt
W
Vt = f ( t )Fig. 3. A box model of the upper 200 m layer of the Japan Sea. V is the volume transport throughTsushima Strait to the Japan Sea. Sd is the salinity of the Tsushima Strait and S is the salinity of theupper 200m layer in the Japan Sea. The volume of the box is W. The fresh water input, R, is given as
precipitation minus evaporation and river discharge.

Fig. 4. Forcing parameters variation in the LGM (30 ka-20 ka) simulation. (a) V-Volume, the volumetransport through Tsushima Strait to the Japan Sea. (b) S-Salinity, the salinity of the upper 200mlayer of the Japan Sea.
The model is forced with the value of variables as Vt = 3 Sv, St = 34. Numerical calculations arecarried out for ten thousand years (t), with various initial conditions. The volume (Vt) decreases withtime due to the low sea level. We assume that the relationship between volume transport through theTsushima Strait and time is linear or nonlinear. The evolution is shown in Fig.4. The salinity values
greatly decrease during the LGM. The final salinity is 22.0 in the case of linear decreasing of volumetransport with time and 24.8 in the case of nonlinear decreasing of volume transport with time. Since
the fresh water value is fixed, a complete shutoff reduces the upper layer salinity to about 10.
References:
Matsui H, Tada R, Oba T. Low-salinity isolation event in the Japan Sea in Response to Eustatic

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Sea-Level drop during the LGM: Reconstruction based on salinity-balance model[J]. The Quaternary
Research(Jpn), 1998,37(3):221-223.
Yanagi T . Water, Salt, Phosphorus and Nitrogen Budgets of the Japan Sea[J]. Journal of
Oceanography, 2002, 58(6):797-804.

Publication/conference presentation
Oral presentation (LaMer):
Title: Low sea surface salinity in the Japan Sea during the last glacial maximum
Lecturer: Kailun Du.
Time: December 3, 2018.
Location: Ehime University.

Perspectives in future
We will clarify the change of volume transport through the Tsushima Strait with sea level
dropping and the impacts of the volume transport through Tsushima Strait on the reduction of sea
surface salinity during the LGM, which can provide reference and basis for paleoceanography
research. We will enhance the cooperation researches and exchanges of faculties and students
between the Ocean University of China and CEMS of Ehime University.

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