Vertical Distribution patterns

Total live assemblage

The persistent severely hypoxic environment at 300 m was reflected in the vertical distribution of live macrofaunal Foraminifera (Table 4.11 and Figure 4.13). In both seasons sampled, bottom-water oxygen was less than 0.5 mll-1 and the ALD5 was < 0.5 cm, with over 93% of all live Foraminifera found in the upper 1 cm sediment layer. Following the SW monsoon, the ALD5 decreased slightly from 0.41 (intermonsoon) to 0.33 (monsoon) and the concentration of live Foraminifera in the upper 1 cm sediment layer increased correspondingly from 93.5% to 97.6% respectively. Less than 7% of all live Foraminifera were found in sediment layers between 1 and 5 cm during each of the seasons sampled.

The main foraminiferal groups

There was little seasonal change in the vertical distribution patterns of the three main foraminiferal groups, calcareous, monothalamous and other agglutinated at the 300- m site (Table 4.11 and Figure 4.13). Calcareous forms maintained a relatively stable vertical distribution pattern between the two seasons. They were restricted to the upper 3 cm of sediment, but were mainly found in the upper 1 cm, increasing from 58.3% of the total live assemblage in the intermonsoon season to 70.8% after the SW summer monsoon. The proportion of non-calcareous Foraminifera (monothalamous and other agglutinated) declined in all sediment layers following the SW monsoon. The colonization depth of other agglutinated forms (multilocular agglutinated forms and ammodiscaceans) decreased from 0-3 cm during the intermonsoon, to 0-2 cm following the SW monsoon. The colonization depth of monothalamous forms displayed a similar trend to the agglutinated forms, decreasing from 0-3 cm preceding the monsoon to 0-2 cm following the monsoon. All live monothalamous forms were found in the upper 0-1 cm sediment layer, unlike calcareous and agglutinated forms, which also occurred in deeper sediment layers.

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Figure 4.13 300-m site. Vertical distribution of live macrofaunal (>300 µm) Foraminifera within the 0-5 cm sediment vertical fraction during both seasons sampled: a) spring intermonsoon, b) SW monsoon. Data are mean values of total live individuals from 4 replicates (25.5 cm2) per season and are presented for major foraminiferal groups. 95% Confidence Intervals are shown. N = Mean live individuals (average of 4 replicate samples of 25.5 cm2). ALD5 = Average Living Depth in 0-5 cm. Mean percentage abundance of live individuals in the 0-1 cm layer is also shown. 0 50 100 150 200 250 0-0.5 cm 0.5-1 cm 1-2 cm 2-3 cm 3-4 cm 4-5 cm a) 300 m. Spring intermonsoon. 0-5 cm. b) 300 m. SW monsoon. 0-5 cm. 0 50 100 150 200 250 300 350 0-0.5 cm 0.5-1 cm 1-2 cm 2-3 cm 3-4 cm 4-5 cm N = 218 ALD = 0.41 0-1 cm = 93.5% 5 N = 311 ALD = 0.33 0-1 cm = 97.6% 5 Lagenina

Table 4.11 300-m site. Mean percentage abundance of live macrofaunal (>300µm) foraminiferal groups at 140m. a) All vertical layers analysed, b) Σ of vertical layers 0-1cm, 1-5cm, 0-5cm. Data are mean values of 4 replicates per season ± 95% Confidence Interval. Underlined data show a significant increase in percentage abundance from intermonsoon to monsoon (P < 0.05, student t-test assuming unequal variances). Grey boxes highlight layers where no live Foraminifera are present. Note the increase in mean percentage abundance of total Foraminifera and calcareous Foraminifera in monsoon samples and a corresponding decline in monothalamous and other agglutinated forms.

a)

300m Mean% Total Live Mean%calcareous Mean%other agglutinated Mean%monothalamous intermonsoon monsoon intermonsoon monsoon intermonsoon monsoon intermonsoon monsoon 0-0.5 80.8±8.7 88.5±3.4 52.5±10.6 66.8±5.5 22.2±4.2 19.3±5.9 7.1±3.4 3.5±2.0 0.5-1 12.6±4.9 7.7±3.2 5.8±3.9 4.0±2.6 5.2±0.6 3.2±2.1 1.6±1.3 0.6±0.4 1-2 5.7±4.4 1.5±0.5 2.3±2.2 0.5±0.3 3.0±2.2 0.6±0.4 0.3±0.4 0.1±0.2 2-3 0.9±1.0 2.0±2.9 0.5±0.6 0.2±0.2 0.5±0.5 0.0±0.0 0.7±0.5 0.0±0.0 3-4 0.0±0.0 0.3±0.3 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.3±0.3 4-5 0.0±0.0 0.1±0.2 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 0.0±0.0 b)

300m Mean% Total Live Mean%calcareous Mean%other agglutinated Mean%monothalamous intermonsoon monsoon intermonsoon monsoon intermonsoon monsoon intermonsoon monsoon 0-1 93.4±5.3 96.3±3.2 58.3±9.0 70.8±7.8 27.4±4.3 22.4±6.4 8.1±3.3 3.0±1.9 1-5 4.9±4.3 4.5±3.1 1.9±1.9 0.7±0.3 2.9±2.5 3.1±3.1 0.1±0.2 0.1±0.2 0-5 100 100 61.1±7.4 71.5±8.0 30.9±5.3 25.5±6.7 9.0±4.1 4.1±2.0

Top-5-ranked species

The top-5-ranked species at 300 m were represented by both calcareous and agglutinated species (Figure 4.14). During the spring intermonsoon season, two calcareous species (Uvigerina ex. gr. semiornata and Globobulimina cf. G. pyrula) and three agglutinated species (Reophax dentaliniformis, Ammodiscus aff. cretaceus and Bathysiphon sp. nov. 1) comprised the top 5 ranked species. The most abundant species U. ex. gr. semiornata, displayed a shallow Average Living Depth (ALD5 = 0.3), with a substantial peak in abundance within the upper 0-0.5 cm sediment layer. All other species displayed a similar trend with the maximum number of individuals in the upper 0-0.5 cm layer. Reophax dentaliniformis, A. aff. cretaceus and B. sp. nov. 1 all had an Average Living Depth of < 0.5 cm (ALD5 = 0.47 cm, 0.33 cm, 0.47 cm

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respectively). However, G. cf. G. pyrula penetrated the deepest, with an Average Living Depth of 0.78 cm; live individuals were found between 0-3 cm sediment depth. Following the SW monsoon, the five most abundant species (again three calcareous and two agglutinated) all displayed a shallow Average Living Depth of < 0.5 cm. Uvigerina ex. gr. semiornata displayed a slight decrease in Average Living Depth (ALD5 = 0.28) following the SW monsoon and all individuals were restricted to the upper 0-0.5 cm sediment layer.

Figure 4.14 300-m site. Vertical distribution of the top-5-ranked live macrofaunal (>300µm) foraminiferal species in the 0-5 cm sediment layer: a) spring intermonsoon (April 2003), b) SW monsoon (October 2003). Data are mean values of 4 replicates per season. 95% Confidence Intervals are shown. Average Living Depth in the 0-5 cm sediment layer (ALD5) is shown for each species.

0 50 100 150 0-0.5 0.5-1 1-2 2-3 3-4 4-5 0 20 40 0 10 20 30 0 5 10 15 0 5 10 15 0 50 100 150 0 20 40 0 10 20 30 0 5 10 15 0 5 10 15 0 - 0.5 cm 0.5 - 1 cm 1 - 2 cm 2 - 3 cm 3 - 4 cm 4 - 5 cm Sediment depth (cm) 0 50 100 150 200 250 0 15 30 45 60 0 10 20 30 0 5 10 15 0 5 10 15 20 0 - 0.5 cm 0.5-1 cm 1 - 2 cm 2 - 3 cm 3 - 4 cm 4 - 5 cm Sediment depth (cm) 0-0.5 cm 0.5-1 cm 1-2 cm 2-3 cm 3-4 cm 4-5 cm Sediment depth (cm) 0 50 100 150 0 20 40 0 10 20 30 0 5 10 15 0 5 10 15 0-0.5 cm 0.5-1 cm 1-2 cm 2-3 cm 3-4 cm 4-5 cm Sediment depth (cm) 0 100 200 0 20 40 60 80 0 10 20 30 0 5 10 15 0 5 10 15 20

Uvigerina Reophax Ammodiscus Globobulimina Bathysiphon

emiornata dentaliniformis retaceus G. pyrula

ex.

gr. s aff. c cf. sp. nov. 1

ALD = 0.35 ALD = 0.475 ALD = 0.335 ALD = 0.785 ALD = 0.475 a) 300 m. Spring intermonsoon.

b) 300 m. SW monsoon.

Uvigerina Reophax Bolivina Globobulimina Reophax

semiornata dentaliniformis dilatata G. pyrula

ex. aff.

gr. cf. sp. 2

Bolivina aff. dilatata displayed a similar trend to Uvigerina ex. gr. semiornata with an Average Living Depth of 0.27. The third calcareous species in the top 5, Globobulimina cf. G. pyrula, displayed a deeper Average Living Depth (ALD5 = 0.49), although this was based on a few individuals found below 0-1 cm. Two species of Reophax (Reophax dentaliniformis and Reophax sp. 2 were present in the top 5 in the monsoonal samples. Both displayed a very similar trend, penetrating fairly deep into the sediment with live individuals found between 0-3 cm sediment depth (Reophax sp. 2, ALD5 = 0.46) and 0-4 cm sediment depth (Reophax dentaliniformis, ALD5 = 0.49).

4.4 Seasonal changes in the live foraminiferal assemblages at the