Water column Particulate Organic Carbon (POC) and Particulate Organic Nitrogen (PON) results from Sediment Traps from R/V Tangaroa cruise 61TG_3052 in the Southern Ocean in 1999 (SOIREE project)

SOIREE Sediment Traps - Water column POC and PON results<br<br>

<b>METHOD</b><br>
Two litre samples filtered through preweighed, precombusted (450&#176;C for 4 hours) GF/F filters;<br>
assumed negligible carbonate so samples non-acidified; whole filters analysed on CHN analyser<br>
<br>
Corrected values were calculated based on a filtered volume of 2 litres, rather than 500 ml<br>
as reported for the initial values<br>
<br>
<b>NOTES</b><br>
1. The initial and OUTSIDE PATCH water column integrated POC values from SOIREE are higher<br>
than expected for Southern Ocean HNLC waters. For example, unpublished data provided by<br>
Wilford Gardner (USA) from the US JGOFS AESOPS transect, show that between 52-72&#176;S 170&#176;W<br>
integrated POC standing stocks (0-50 m) in summer ranged from 3002-14413 mgC/m2 in Dec 1997<br>
and 3603-10209 mgC/m2 in Jan 1998 SOIREE POC (MLD integrated) range from 4500-6200 mgC/m2<br>
outside the iron-fertilised patch which were not substantially different from that measured<br>
inside the patch during the SOIREE bloom (5100-8500 mgC/m2)<br>
<br>
2. There is no obvious indication from either sampling or analytical techniques that the POC<br>
values are artificially inflated due to sample handling, etc.<br>
<br>
3. Charette & Buesseler (2000, G3) suggest that a previous export event must have occurred prior<br>
to SOIREE due to a substantial 234Th deficit relative to 238U, which might explain the SOIREE POC<br>
results. Since there is no indication from daily SeaWiFS images of a surface bloom from Nov 1998-Jan 1999<br>
(C. Law pers. comm., 1999), nor any \"memory\" of such an event in the pCO2 data (Watson et al., 2000, Nature),<br>
Charette & Buesseler (2000) suggested that such a bloom is likely to have been a subsurface feature,<br>
or that there was a significant delay in export<br>
<br>
4. \"Live\" biological carbon in HNLC waters outside the patch represented a significant or similar<br>
amount of the organic carbon that was measured in the water column, ranging from 78-100% of the<br>
MLD-integrated POC (see Table A below). If we assume that the water column samples would have sampled<br>
only the phytoplankton and the microzooplankton (and not heterotrophic bacteria and mesozooplankton)<br>
then this proportion decreases to 40-60% but is still relatively substantial.<br>
<br>
5. POC values inside and outside the SOIREE patch were similar despite 6-fold and 3-fold increases in<br>
chlorophyll a concentrations and phytoplankton abundance, respectively, inside the iron-fertilised patch<br>
(Boyd et al., 2000, Nature)<br>
<br>
6. Therefore, we conclude that perhaps there was a significant POC component in the water column at<br>
the time that the SOIREE site was occupied, representing relict organic material derived from a previous<br>
bloom/export event.<br>
<br>
7. Given the uncertainties, however, it is wise to treat the interpretation of the above POC data with caution.<br>
<br>
<pre>
<b>Table A</b> mixed layer (0-65 m)
col integrated POC
OUT stations only mg C m-2 mg C m-2 % %

STATION phyto hbact microzoo mesozoo total POC water column Difference (ALL) Diff (phyto + micro only)
12-Feb-99 T1141/1 1595 504 772 1600 4471 5615 79.6 42.2
16-Feb-99 T1152/1 2023 346 620 1600 4589 5881 78.0 44.9
18-Feb-99 T1157/1 1595 290 616 1600 4101 5157 79.5 42.9
21-Feb-99 T1168/1 1885 374 706 1600 4565 4564 100.0 56.8
</pre>

<b>SOIREE沉积物捕集器——水柱颗粒有机碳（Particulate Organic Carbon, POC）与颗粒有机氮（Particulate Organic Nitrogen, PON）结果</b>

<b>实验方法</b>
取2升水样，经预先称重、预灼烧（450℃下灼烧4小时）的GF/F滤膜过滤；因预估碳酸盐含量可忽略不计，故样品无需酸化；将整张滤膜置于碳氢氮（CHN）分析仪上进行分析。
校正值基于过滤体积2升计算，而非初始值报告中所用的500毫升。

<b>备注</b>
1. SOIREE项目中初始及斑块外的水柱积分颗粒有机碳值，高于南大洋高营养盐低叶绿素（High-Nutrient Low-Chlorophyll, HNLC）海域的预期水平。例如，美国的威尔福德·加德纳（Wilford Gardner）提供的未发表数据来自美国全球海洋通量联合研究（Joint Global Ocean Flux Study, JGOFS）的AESOPS断面，该数据显示：在南纬52°-72°、西经170°海域，1997年12月夏季0-50米水深的积分POC储量为3002-14413 mgC/m²，1998年1月该范围为3603-10209 mgC/m²；而SOIREE项目中铁肥化斑块外的混合层深度（Mixed Layer Depth, MLD）积分POC值为4500-6200 mgC/m²，与SOIREE藻华期间斑块内部测得的POC值（5100-8500 mgC/m²）并无显著差异。
2. 无论是采样还是分析技术层面，均未发现明显迹象表明POC值因样品处理等操作被人为高估。
3. 查雷特（Charette）与布瑟勒（Buesseler）于2000年发表于《G3》的研究指出，相较于铀-238（²³⁸U），海水中钍-234（²³⁴Th）存在显著亏损，这表明在SOIREE项目开展前曾发生过一次碳输出事件，该事件或可解释本次SOIREE的POC结果。由于1998年11月至1999年1月的每日SeaWiFS卫星影像未显示表层藻华迹象（C. Law，私人通信，1999年），且二氧化碳分压（pCO₂）数据中也无此类事件的相关记录（Watson等，2000年，《Nature》），因此查雷特与布瑟勒（2000年）提出，该藻华可能为次表层现象，或是碳输出过程存在显著延迟。
4. 斑块外HNLC海域的"Live"生物碳占水柱测得有机碳的比例较高甚至相当，为MLD积分POC的78%-100%（详见下表A）。若假设水柱样品仅采集了浮游植物和微型浮游动物（而非异养细菌与中型浮游动物），则该比例将降至40%-60%，但仍处于较高水平。
5. 尽管铁肥化斑块内的叶绿素a浓度与浮游植物丰度分别提升了6倍与3倍，但SOIREE项目斑块内外的POC值并无显著差异（Boyd等，2000年，《Nature》）。
6. 因此，我们认为在SOIREE项目站位开展采样时，水柱中可能存在大量POC组分，其为先前藻华或碳输出事件遗留的有机物质。
7. 然而考虑到存在诸多不确定性，对上述POC数据的解读需谨慎行事。

<pre>
<b>表A</b> 混合层（0-65 m）
柱积分POC
仅外站数据 mg C m⁻² mg C m⁻² 百分比 百分比

站位 浮游植物 异养细菌 微型浮游动物 中型浮游动物 总量 水柱POC 总差值 仅浮游植物+微型浮游动物差值
1999年2月12日 T1141/1 1595 504 772 1600 4471 5615 79.6 42.2
1999年2月16日 T1152/1 2023 346 620 1600 4589 5881 78.0 44.9
1999年2月18日 T1157/1 1595 290 616 1600 4101 5157 79.5 42.9
1999年2月21日 T1168/1 1885 374 706 1600 4565 4564 100.0 56.8
</pre>