Photochemical Alteration of Dissolved Organic Nitrogen in the Surface Ocean of the North Atlantic

16
Max Jacobson Daniel Sigman Katye Altieri Sarah Fawcett

description

Photochemical Alteration of Dissolved Organic Nitrogen in the Surface Ocean of the North Atlantic. Max Jacobson Daniel Sigman Katye Altieri Sarah Fawcett. Background: A Discrepancy. Sargasso sea water has

Transcript of Photochemical Alteration of Dissolved Organic Nitrogen in the Surface Ocean of the North Atlantic

Max JacobsonDaniel SigmanKatye Altieri

Sarah Fawcett

Background: A DiscrepancySargasso sea water has

<30nM ammoniumBarely measurable

Ammonia effluxes from the surface of the oligotrophic oceanic gyre

The measured efflux is significantly higher than the efflux calculated by Henry’s law

(Johnson et al., 2008, Lipschultz 2001)

NO3-

NH4+

DON NH4+

ParticlesNH4HSO4

(NH4)2SO4

NH4NO3

NaNO3

NH3(g)

Rain [NH4+ ] = 3.5 μM

NH4+ in the Nitrogen cycle

4 μM <30 nM

Oceanic concentrations from the Bermuda Atlantic Time-series Study (BATS)

Lipschultz 2001, Knapp et al., 2005

Project goalTo test the hypothesis that the photo-

oxidation of the high concentration surface DON pool contributes to ammonia efflux from the subtropical surface ocean

Testing the hypothesisDesign an apparatus and/or system to

demonstrate the conversion of dissolved organic nitrogen (DON) into ammonium.

Test the closed system at Princeton and test the open system at the Bermuda Institute of Ocean Sciences.

MethodsAcidified filters to capture NH3 efflux:

Filter impregnation (Quinn 1990)

Extracted captured NH4+ from filters – sonication

Collected and filtered Sargasso seawater using 8L Niskin bottles

Orthophthalaldehde (OPA) fluorescence techniques for measuring nanomolar concentrations of NH4+ (Holmes et al 1999)

Irradiated systems in ambient sunlight with dark control

OPA FluorescenceMeasures nM

concentrations of ammonium

Very accurateExample: Standard

curve with concentrations 0, 10, 25, 100, 250, and 1000 nM

y = 202.1x + 9279.2R² = 0.9998

0

50000

100000

150000

200000

250000

0 500 1000 1500Ra

w fl

uo

res

ce

nce

un

its

(RF

U)

Concentration (nM)

6/7/11 Standard Curve

The Closed System

Testing the Closed SystemFilters were exposed to air on a lab bench for

10, 20, 30, and 40 minutes to investigate contamination

Filters exposed to air for 10 minutes were stored in Ziploc bags for 10, 20, 30, and 40 minutes, 24 and 48 hours to assess contamination associated with storage

One filter was left in the closed system and another filter was left in a fume hood overnight to confirm that the system was air tight

The experiment was run with two bottles: one filled with 10mM NH4+ and the other with HPW

ResultsAir exposure

contaminated filters

Storing in ziploc did not contaminate filters

The closed system is definitely airtight: The filter left in the fume hood had several orders of magnitude more NH4+ than that stored in the closed system

0

50

100

150

200

250

300

350

400

450

0 5 10 15 20 25 30 35 40 45

[NH

4+

] (n

M)

Time (minutes)

Exposure

Times

10min

Linear (Times)

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35

[NH

4+

]

Time in bag

Ziploc

Time(minutes)

Time(minutes)

[NH

4+]

[NH

4+]

Exposure

Ziploc

The Open SystemVacuum pump

Filter packs (removes ammonia from air)

Ring Stand and clamps

Reflux

Condenser

Filters (capture ammonium)

Testing the Open SystemPhysically construct the system

Develop and test the standard operating procedure in order to optimize the performance of the open system

Incubated filtered Sargasso Sea water collected during scientific cruise under sunlight and dark conditions

Seawater collectionSeawater was collected aboard the R/V Stommel using Niskin bottles and transferred to 4L polycarbonate bottles. The water was filtered through a 0.2 μm polycarbonate filter using vacuum filtration.

Seawater was collected aboard the R/V Atlantic Explorer by inline filtration directly from the ship’s underway system.

Lessons LearnedThe temperature controlled experiments were

supposed to be run on the Atlantic Explorer 2 day cruise. However, it rained continuously and irradiation experiments were not possible.

Ammonium samples could not be analyzed at BIOS. The samples were frozen and brought back to Princeton.

The fluorometer was stolen, and the samples could not be analyzed until it was replaced.

Results from the open system were inconclusive: contamination and/or detection limit problems (see above)

SummaryClosed system: airtight limiting contamination

from ambient air. Could be useful for concept testing if modified to increase air/water surface interaction.

Open system: more representative , can control temperature, enhance air/water surface interaction

Future workContinue experimenting with open systemAmend with higher ammonium concentrationAnalyze samples same day to minimize storage

and/or contamination issues

AcknowledgementsPrinceton Environmental Institute

Bermuda Institute of Ocean SciencesAndrew Peters

Karen EllisAmy Gobel

Rosie Zhang