Amino sugars (AS) are important constituents of organic matter. However, very little is known about their cycling in marine waters. In this research, we assessed the distribution and cycling of these compounds in waters of the Bay of Bengal. For this purpose, samples of suspended particu late matter (SPM) were collected from 8 depths (surface to 1000 m) at 6 locations during the 166th cruise of the ORV Sagar Kanya in the Bay of Bengal in July/August 2001. The SPM samples were analysed for particulate organic carbon (POC), particulate nitrogen (PN) and AS concentrations and composition. The AS varied between 0.4 and 17.5 nmol/l. Concentrations were high in the surface waters and generally decreased with increasing depth. AS concentration decreased from the south to north. AS accounted for 0.01 to 0.71% and 0.05 to 2.37% of POC and PN, respectively. Rapid decrease in AS-C% and AS-N% with depth indicates that these compounds were preferentially degraded relative to bulk POC and PN. The composition of AS suggests that glucosamine (GLU-N) and galactosamine (GAL-N) were present in the surface SPM samples, and their abundance decreased from surface downwards. Relatively, low values of GLU-N/GAL-N ratio indicate that the organic matter was mostly derived from the detritus of micro-organisms. Our data suggest that chitin, a polymer of the glucosamine produced by many marine organisms was not the major source of AS in the Bay. Rapid cycling of these compounds indicates their importance in the cycling of nitrogen in marine waters

Surface seawater samples were collected over a period of 27 months at a shallow water station in Dona Paula bay from 1998–2000. The samples were analyzed to assess the seasonal variations, inter-annual variability and the contributions of:

A distinct inter-annual variability was observed with an increase in the bacterial abundance, chlorophylla (Chl a), TEP and Sal-PCHO and their greater contribution to particulate organic carbon during May 1998–1999 than in June 1999–July 2000. Overall, there was no statistically significant correlation of TEP with phytoplankton biomass (Chl a), Sal-PCHO, CPCHO and hydrodynamic conditions. A weak inverse correlation was observed between TEP and TBA (r = −0.397;p < 0.05) but the role of TEP as a C-source for bacteria was not evident. Both Sal-PCHO and CPCHO appeared to be two distinct forms of carbohydrates. Unlike CPCHO, Sal-PCHO concentrations showed a positive trend with Chla and significant linear correlation with bacterial abundance (r = 0.44,p < 0.007,n = 48), indicating that Sal-PCHO as carbon source might have supported bacterioplankton abundance. The mean %TEP-C contribution to the annual average organic carbon for 1998–2000 was 6.9% ± 5.8%, next only to phytoplankton-C (33.1 ± 22.1%) and greater than bacterial-C (4.6% ± 4.6%) or carbohydrate-C (< 3.8%). Despite its greater contribution to the organic carbon pool, the contribution of TEP-C to the benthic carbon demand and its fate in the study area could not be ascertained in this study.

Suspended particulate matter (SPM)of surface seawaters was collected during December 2003 to October 2004 at 10 stations in the Bay of Bengal,and analyzed for particulate organic carbon (POC),total particulate nitrogen (TPN),total particulate carbohydrate (TPCHO)and total particulate uronic acids (TPURA).The concentrations of POC,TPCHO and TPURA varied from 4.80 to 29.12,0.85 to 4.24,0.09 to 0.91 𝜇 C,respectively.The TPCHO-C and TPURA-C accounted for 6.6 –32.5%and 0.87 –3.65%of POC.The trends observed for the distribution of these compounds were generally similar to those recorded for the distribution of chlorophyll 𝑎 (Chl 𝑎) .The C/N ratios varied from 3.2 to 22.3 with most of the values being > 10.This suggests that the organic matter was mostly derived from phytoplankton and bacteria.Relatively low C/N ratios and high TPCHO yield imply that freshly derived organic matter was present during SWM and FIM.Our data suggest that the quality and quantity of organic matter varied spatially and seasonally.

Carbohydrates including uronic acids are among the active components of dissolved organic carbon, and play an important role in biogeochemical cycling of organic carbon in marine environments. In order to understand their distribution, concentrations of total dissolved carbohydrate (TCHO), dissolved polysaccharide (PCHO), dissolved monosaccharide (MCHO), and dissolved uronic acid (URA) were measured in the Mandovi estuary, west coast of India during the monsoon and premonsoon seasons. The estuary experienced nearly fresh water condition during the monsoon season and marine condition during the pre-monsoon season. Concentrations of TCHO, MCHO and URA ranged from 17.7 to 67.3 𝜇M C, 4.1 to 15.5 𝜇M C and 2.3 to 10.8 𝜇M C, and their contribution to dissolved organic carbon (DOC) varied from ∼11 to 60%, 2.5 to 9.7%, and 1.8 to 5.3%, respectively. PCHO accounted for ∼52 to 92% of the TCHO. Generally, concentrations and yields of TCHO species were greater during the monsoon season. Phytoplankton abundance and bacterial cell numbers influenced the distribution of TCHO in the pre-monsoon season but not during the monsoon season. Transport of TCHO rich (11 to 60%) dissolved organic matter from the Mandovi estuary to the coastal waters during the monsoon season may affect ecosystem function by fueling biological activity of heterotrophic micro-organisms.