**3.1 Dissolved Oxygen (DO)**

The vertical changes of DO in water column are shown by selecting some of the stations from each of the three (western-central-eastern) basins where the variations are significant (Figure 3). In station (R), DO concentrations are between 7.4-10.7 mgl-1 for the upper layer, and 1.1-1.5 mgl-1 in the lower layer during the sampling period between August 1999 to August 2000 (Figure 3), which are similar to vertical DO concentrations of the Marmara Sea (Ünlüata and Özsoy, 1986; Ünlüata et al., 1990; Doğan et al., 2000). Depth profile of DO concentration in İzmit Bay displays a sharp decrease at about 20 m below the surface in the western and the central basins, following the water stratification during late summer and autumn (Güven et al., 2000) (Figure 3). In February the gradual decline of DO occurs at about 30 m water depth.

DO concentration of the water column in the eastern basin indicates a more gentle profile, probably due to the vertical mixing of the two layers (Oğuz and Sur, 1986; Altok et al., 1996) in shallow depths. DO concentration of the upper layer in İzmit Bay varies in a range between 4.5 to 12.1 mgl-1 during August 1999-2000 (Figure 4a and b). Saturated DO occurs in the upper layer locally at the eastern basin in October 1999 (Figure 4a, 5). The saturation concentration of DO (SDO) values are determined by the solubility oxygen in sea water as a function of the concurrently measured values of temperature and salinity (Figure 2, 5 and 6). The highest DO concentrations were measured in February 2000 (Figure 4b), whereas the lowest DO concentrations were measured in September 1999 after the earthquake. The distribution of DO concentration in the upper layer is almost homogeneous in August and September 1999. From October 1999 to February 2000, DO concentration of the upper layer significantly increases. The increase of DO concentration occurred subsequently following the maximum phytoplankton bloom in October (Güven et al., 2000). DO concentrations range between 7.9-14.5 mgl-1 in October 1999, displaying the highest value in the eastern basin (Figure 4a and 5). The distribution of DO concentration in the upper layer becomes almost homogeneous with a range of 9.0-10.4 mgl-1 in December 1999 and slightly increases (10.19-12.12 mgl-1) in February 2000. DO concentrations in the upper layer decrease (6.69- 10.57 mgl-1) in spring (May-2000, Figure 4b) and are lower in the eastern basin compare to the central and the western basins of İzmit Bay. In August 2000, DO concentrations lie between 5.0 and 9.4 mgl-1, being relatively high in the central basin.

DO content of the lower layer is significantly lower than that of the upper layer, throughout the sampling period (Figure 3). In August 1999, after the earthquake DO concentrations of the lower layer ranges between 0.0-1.46 mgl-1. DO concentration below the detection limits (<0.03 mgl-1) was measured in areas where the water depth is deeper than 100 m and also in the eastern basin (Figure 7a and b). The lowest DO concentration ranges were measured in September 1999. The deficiency of DO is mostly accompanied with the presence of DHS and

The precision of the "total" metal analyses and the different selective extraction steps is better than 10% and 15%, respectively, at 95% significance level. The accuracy of the analyses were checked by analyzing the AQCS (lake sediment SL-1 and SL-7), IAEA405 and BCR (light sandy soil CRM 142) reference materials (Table 1). The metal values were normalized to eliminate the grain-size effects using metal/Al ratios (e.g., Loring Rantala,

The vertical changes of DO in water column are shown by selecting some of the stations from each of the three (western-central-eastern) basins where the variations are significant (Figure 3). In station (R), DO concentrations are between 7.4-10.7 mgl-1 for the upper layer, and 1.1-1.5 mgl-1 in the lower layer during the sampling period between August 1999 to August 2000 (Figure 3), which are similar to vertical DO concentrations of the Marmara Sea (Ünlüata and Özsoy, 1986; Ünlüata et al., 1990; Doğan et al., 2000). Depth profile of DO concentration in İzmit Bay displays a sharp decrease at about 20 m below the surface in the western and the central basins, following the water stratification during late summer and autumn (Güven et al., 2000) (Figure 3). In February the gradual decline of DO occurs at

DO concentration of the water column in the eastern basin indicates a more gentle profile, probably due to the vertical mixing of the two layers (Oğuz and Sur, 1986; Altok et al., 1996) in shallow depths. DO concentration of the upper layer in İzmit Bay varies in a range between 4.5 to 12.1 mgl-1 during August 1999-2000 (Figure 4a and b). Saturated DO occurs in the upper layer locally at the eastern basin in October 1999 (Figure 4a, 5). The saturation concentration of DO (SDO) values are determined by the solubility oxygen in sea water as a function of the concurrently measured values of temperature and salinity (Figure 2, 5 and 6). The highest DO concentrations were measured in February 2000 (Figure 4b), whereas the lowest DO concentrations were measured in September 1999 after the earthquake. The distribution of DO concentration in the upper layer is almost homogeneous in August and September 1999. From October 1999 to February 2000, DO concentration of the upper layer significantly increases. The increase of DO concentration occurred subsequently following the maximum phytoplankton bloom in October (Güven et al., 2000). DO concentrations range between 7.9-14.5 mgl-1 in October 1999, displaying the highest value in the eastern basin (Figure 4a and 5). The distribution of DO concentration in the upper layer becomes almost homogeneous with a range of 9.0-10.4 mgl-1 in December 1999 and slightly increases (10.19-12.12 mgl-1) in February 2000. DO concentrations in the upper layer decrease (6.69- 10.57 mgl-1) in spring (May-2000, Figure 4b) and are lower in the eastern basin compare to the central and the western basins of İzmit Bay. In August 2000, DO concentrations lie

DO content of the lower layer is significantly lower than that of the upper layer, throughout the sampling period (Figure 3). In August 1999, after the earthquake DO concentrations of the lower layer ranges between 0.0-1.46 mgl-1. DO concentration below the detection limits (<0.03 mgl-1) was measured in areas where the water depth is deeper than 100 m and also in the eastern basin (Figure 7a and b). The lowest DO concentration ranges were measured in September 1999. The deficiency of DO is mostly accompanied with the presence of DHS and

between 5.0 and 9.4 mgl-1, being relatively high in the central basin.

1992).

**3. Results** 

**3.1 Dissolved Oxygen (DO)** 

about 30 m water depth.

Fig. 3. Vertical distribution of DO and DHS along the water column in various stations of İzmit Bay.

The Effect of Marmara (Izmit) Earthquake on the Chemical

40.80 February/2000

Oceanography and Mangan Enrichment in the Lower Layer Water of Izmit Bay, Turkey 255

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

Fig. 4b. Spatial distribution of DO (mgl-1) in the upper layer of İzmit Bay during February to

is discussed below. The local anoxic conditions continue in September and October 1999 (Figure 7a), mainly in the central basin with DO concentration range of 0.0-3.4 mgl-1 and 0.0- 7.9 mgl-1, respectively. In December 1999, DO concentration of the lower layer generally increases (0.0-8.3 mgl-1), but in only one station (17) no DO was lower than the detection limits (Figure 7a). The distribution pattern of DO concentration in the lower layer displays similar behavior in February and May 2000 (Figure 7b) with ranging between 0.0-8.2 mgl-1 and 0.0-8.8 mgl-1, respectively. Relatively higher DO concentrations are close to the northern coast of İzmit Bay (Figure 7a and 7b). DO concentration of the lower layer decrease in

August/2000 4.50

4.90 5.30 5.70 6.10 6.50 6.90 7.30 7.70 8.10 8.50 8.90 9.30 9.70 10.10 10.50 10.90 11.30 11.70 12.10

mg/l

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

May/2000

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

40.70

August 2000.

August 2000, ranging between 0.0-3.6 mgl-1.

40.80

40.70

40.80

40.70

Fig. 4a. Spatial distribution of DO (mgl-1) in the upper layer of İzmit Bay during August to December 1999.

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

Fig. 4a. Spatial distribution of DO (mgl-1) in the upper layer of İzmit Bay during August to

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

October/1999

4.50 4.90 5.30 5.70 6.10 6.50 6.90 7.30 7.70 8.10 8.50 8.90 9.30 9.70 10.10 10.50 10.90 11.30 11.70 12.10

mg/l

> 12

40.80 August/1999

40.80 September/1999

40.80 December/1999

40.70

40.70

40.70

December 1999.

40.70

40.80

Fig. 4b. Spatial distribution of DO (mgl-1) in the upper layer of İzmit Bay during February to August 2000.

is discussed below. The local anoxic conditions continue in September and October 1999 (Figure 7a), mainly in the central basin with DO concentration range of 0.0-3.4 mgl-1 and 0.0- 7.9 mgl-1, respectively. In December 1999, DO concentration of the lower layer generally increases (0.0-8.3 mgl-1), but in only one station (17) no DO was lower than the detection limits (Figure 7a). The distribution pattern of DO concentration in the lower layer displays similar behavior in February and May 2000 (Figure 7b) with ranging between 0.0-8.2 mgl-1 and 0.0-8.8 mgl-1, respectively. Relatively higher DO concentrations are close to the northern coast of İzmit Bay (Figure 7a and 7b). DO concentration of the lower layer decrease in August 2000, ranging between 0.0-3.6 mgl-1.

The Effect of Marmara (Izmit) Earthquake on the Chemical

Oceanography and Mangan Enrichment in the Lower Layer Water of Izmit Bay, Turkey 257

Fig. 6. Depth profile of salinity and temperature distribution along the water column of

some selected stations from İzmit Bay (from Güven et al., 2000).

Fig. 5. Oxygen deficiency profiles in some selected stations of İzmit Bay.

Fig. 5. Oxygen deficiency profiles in some selected stations of İzmit Bay.

Fig. 6. Depth profile of salinity and temperature distribution along the water column of some selected stations from İzmit Bay (from Güven et al., 2000).

The Effect of Marmara (Izmit) Earthquake on the Chemical

40.80 February/2000

40.80 August/2000

**3.2 Dissolved Hydrogen Sulfide (DHS)** 

40.70

40.70

40.70

August 2000.

40.80

Oceanography and Mangan Enrichment in the Lower Layer Water of Izmit Bay, Turkey 259

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

Fig. 7b. Spatial distribution of DO (mgl-1) in the lower layer of İzmit Bay during February to

The presence of DHS is limited with certain stations and in the lower layer. DHS formation develops both in the shallow area of the eastern basin (maximum 30 m) and relatively deep areas of the central basin. DHS is detected in stations 27, 29, 30 and 31 in the eastern basin, and 8C, 17, 19, 20, 23 and 24 in the central basin (Figure 1, Table 1). In the station 25 situated at the connecting small strait between the eastern and the central basin, measurable DHS exists in the lower layer. DHS concentrations vary in between 0.06-1.25 mgl-1, reaching to their maximum in the lower layer of station 17. No DHS data available for the sampling period of August 1999 after the Earthquake. DHS concentration in October 1999 reaches to 1.14 mgl-1 in the eastern basin (station 30) (Figure 3). In general, DHS appears at a water

May/2000

0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 4.40 4.80 5.20 5.60 6.00 6.40 6.80 7.20 7.60 8.00 8.40 8.80

mg/l

Fig. 7a. Spatial distribution of DO (mgl-1) in the lower layer of İzmit Bay during August to December 1999

No data

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

October/1999

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

29.20 29.30 29.40 29.50 29.60 29.70 29.80 29.90

Fig. 7a. Spatial distribution of DO (mgl-1) in the lower layer of İzmit Bay during August to

40.70

40.70

40.70

40.70

December 1999

40.80

40.80 August/1999

40.80 September/1999

40.80 **December/1999**

Fig. 7b. Spatial distribution of DO (mgl-1) in the lower layer of İzmit Bay during February to August 2000.

#### **3.2 Dissolved Hydrogen Sulfide (DHS)**

0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 4.40 4.80 5.20 5.60 6.00 6.40 6.80 7.20 7.60 8.00 8.40 8.80

mg/l

The presence of DHS is limited with certain stations and in the lower layer. DHS formation develops both in the shallow area of the eastern basin (maximum 30 m) and relatively deep areas of the central basin. DHS is detected in stations 27, 29, 30 and 31 in the eastern basin, and 8C, 17, 19, 20, 23 and 24 in the central basin (Figure 1, Table 1). In the station 25 situated at the connecting small strait between the eastern and the central basin, measurable DHS exists in the lower layer. DHS concentrations vary in between 0.06-1.25 mgl-1, reaching to their maximum in the lower layer of station 17. No DHS data available for the sampling period of August 1999 after the Earthquake. DHS concentration in October 1999 reaches to 1.14 mgl-1 in the eastern basin (station 30) (Figure 3). In general, DHS appears at a water

The Effect of Marmara (Izmit) Earthquake on the Chemical

degree in the central basin, during the formation of DHS.

respectively, contain DHS.

**3.3 pH** 

**3.4 Metals** 

productivity.

**3.4.1 Water column** 

Oceanography and Mangan Enrichment in the Lower Layer Water of Izmit Bay, Turkey 261

DHS is continuously detected in station 17 from the central basin in all the sampling periods, being highest in October 1999 and lowest in May 2000. The occurrence of DHS corresponds to depth interval of 100-160 m (bottom) during October and December 1999. In February 2000, DHS concentration is limited with the lower 10 m water column, increasing to 1.25 mgl-1 at the bottom. The thickness of DHS formation layer slightly increases to 20 m in May 2000, however the concentrations are reduced compare to February 2000 (Figure 3, Table 2). In August 2000, both concentration and thickness of DHS formation of the lower layer in station 17 increase. In spite of continuous presence of DHS in station 17, it occurs solely in October 1999 in the other stations of the central basin, and never reaches to 1 mgl-1 (Figure 3, Table 1). DHS is detected mainly at the very close to bottom (2 m above the sea floor) of the lower layer in most of the stations in the central basin, however the lower 25 m and 15 m of the water column in station 20 and 8C,

The highest pH values were measured in October 1999 and May 2000 throughout the water column in İzmit Bay, and were particularly high in the eastern basin (Figure 8 and 9). The lowest pH values, on the other hand, correspond to sampling period of August 2000. pH values significantly decrease from 8.5 to 7.1 mainly in the eastern basin and to a lesser

Iron concentrations range between <4 mg/l and 21 mg/l along the water column in İzmit Bay (Table 3). The highest values are measured after the Earthquake (October-1999). High dissolved Fe concentrations indicate reduction of Fe-oxides by bacteria during mineralization of organic carbon in the sediment and diffusion into bottom waters (Nealson, 1982; Lovley and Phillips, 1988; Nealson and Myers, 1990). Fe values are decrease in May and August 2000 where Fe limitation is thought to control phytoplankton

Manganese concentrations vary between <1 and 123 mg/l in water column of the Bay (Table 3). The values increased in lower layer water and near the sediment-water interface in eastern and central basins. This was attributable to the degradation of settling organic carbon (Nealson, 1982; Nealson and Saffarini, 1994; Nealson and Myers, 1990). Manganese oxides were reduced to dissolved Mn+2, which diffused from the sediment into the water column occurring the anoxic conditions. The lowest Mn values are obtained in December 1999 and February 2000. In these periods, oxygen-rich waters of Marmara Sea (Mediterranean originating) flow into the Bay. Thus, Mn-oxides are occurred and flocculated in water column with reoxidation of dissolved Mn in more oxygenated waters. Lead concentrations range between <0.8 and 1.8 mg/l in the Bay waters (Table 3). The

Copper concentrations vary between <0.4 and 7.4 mg/l along the water column of the Bay (Table 3). The high values shows that Cu was mainly affected by redox reactions involving Mn and Fe in bottom waters of the eastern and central basins. The lowest Cu concentrations are measured in occurring the extreme phytoplankton blooms periods especially in these regions.

highest values are suggested that atmospheric and anthropogenic inputs.

depth of 20 m in the shallow parts of the eastern basin, with the exception of station 29 where DHS exists up to 10 m to the surface. In December, DHS formation occurs only in stations 27 and 29 and disappears in the other stations. During winter and spring sampling period, no DHS is detected in the eastern basin. Low DHS concentration (0.06 and 0.23 mgl-1) is found in stations 27 and 30 in August 2000.


(\*) No detectable DHS

Table 2. DHS concentrations in the lower layer of the eastern and the central basins of İzmit Bay.

DHS is continuously detected in station 17 from the central basin in all the sampling periods, being highest in October 1999 and lowest in May 2000. The occurrence of DHS corresponds to depth interval of 100-160 m (bottom) during October and December 1999. In February 2000, DHS concentration is limited with the lower 10 m water column, increasing to 1.25 mgl-1 at the bottom. The thickness of DHS formation layer slightly increases to 20 m in May 2000, however the concentrations are reduced compare to February 2000 (Figure 3, Table 2). In August 2000, both concentration and thickness of DHS formation of the lower layer in station 17 increase. In spite of continuous presence of DHS in station 17, it occurs solely in October 1999 in the other stations of the central basin, and never reaches to 1 mgl-1 (Figure 3, Table 1). DHS is detected mainly at the very close to bottom (2 m above the sea floor) of the lower layer in most of the stations in the central basin, however the lower 25 m and 15 m of the water column in station 20 and 8C, respectively, contain DHS.

### **3.3 pH**

260 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

depth of 20 m in the shallow parts of the eastern basin, with the exception of station 29 where DHS exists up to 10 m to the surface. In December, DHS formation occurs only in stations 27 and 29 and disappears in the other stations. During winter and spring sampling period, no DHS is detected in the eastern basin. Low DHS concentration (0.06 and 0.23 mgl-1) is

> December 1999

February 2000

May 2000 August 2000

found in stations 27 and 30 in August 2000.

Sampling depth (m)

October 1999

25 40 30 0.07 \* \* \* \* 38 0.21 \* \* \* \* 27 31 20 0.53 \* \* \* \* 25 0.60 0.14 \* \* \* 29 0.71 0.40 \* \* 0.23 29 18 10 0.43 \* \* \* \* 15 0.50 \* \* \* \* 17 0.85 0.24 \* \* \* 30 29 20 0.45 \* \* \* \* 24 0.71 \* \* \* \* 27 1.14 \* \* \* 0.06 31 30 20 0.28 \* \* \* \* 25 0.28 \* \* \* \* 27 0.36 \* \* \* \*

17 160 100 0.57 0.11 \* \* \* 110 0.81 0.11 \* \* \* 120 0.81 0.11 \* \* 0.43 130 0.92 0.21 \* \* 0.48 140 1.11 0.21 \* 0.11 0.59 150 - - 0.60 0.28 0.81 152 - - 0.89 - - 157 1.25 1.12 1.25 0.32 0.90 8C 116 100 0.64 \* \* \* \* 114 0.93 \* \* \* \* 19 29 25 0.40 \* \* \* \* 20 106 75 0.28 \* \* \* \* 80 0.40 \* \* \* \* 90 0.43 \* \* \* \* 102 0.71 0.32 \* \* \* 23 43 38 0.28 \* \* \* \* 24 57 53 0.28 \* \* \* \*

Table 2. DHS concentrations in the lower layer of the eastern and the central basins of İzmit

The central basin Station Water

The eastern basin

(\*) No detectable DHS

Bay.

depth (m)

> The highest pH values were measured in October 1999 and May 2000 throughout the water column in İzmit Bay, and were particularly high in the eastern basin (Figure 8 and 9). The lowest pH values, on the other hand, correspond to sampling period of August 2000. pH values significantly decrease from 8.5 to 7.1 mainly in the eastern basin and to a lesser degree in the central basin, during the formation of DHS.
