1. Introduction
一、简介

In the lower atmosphere, iodine is involved in catalytic ozone destruction cycles and particle formation reactions that impact upon both the oxidising capacity of the atmosphere and the Earth's radiative balance.^1–7 Tropospheric ozone is a greenhouse gas and is harmful to both human health and vegetation, including food crops. As a key oxidant, ozone is also involved in reaction cycles that remove hydrocarbons from the troposphere. A detailed understanding of the controls on tropospheric ozone levels is thus a major goal in atmospheric chemistry. Atmospheric iodine chemistry also has potential to perturb the balance of other important species such as peroxy radicals and nitrogen oxides,^6,8 and may enhance rates of mercury oxidation and deposition at high latitudes.⁸ A key species in these chemical cycles is the iodine oxide (IO) radical, which may also be involved in particle nucleation events where levels are sufficiently high.^7,9–12 The particles formed in such events have potential to act as cloud condensation nuclei, and so can indirectly affect climate via impacts on the radiative properties of clouds. Iodine is also an essential nutrient for humans and many other animals, deficiency of which is the leading cause of preventable brain damage in children.¹³ Sea-to-air transfer, followed by atmospheric transport and deposition onto land, is an important pathway by which iodine can enter the human food chain. It is also a route by which radionuclides of iodine discharged (intentionally or accidentally) to the oceans from nuclear facilities may be returned to the terrestrial environment.
在低层大气中，碘参与催化臭氧破坏循环和颗粒形成反应，影响大气的氧化能力和地球的辐射平衡。 ^1-7对流层臭氧是一种温室气体，对人类健康和包括粮食作物在内的植被有害。作为一种关键的氧化剂，臭氧还参与从对流层去除碳氢化合物的反应循环。因此，详细了解对流层臭氧水平的控制是大气化学的一个主要目标。大气中的碘化学也有可能扰乱其他重要物质的平衡，例如过氧自由基和氮氧化物^6,8 ，并可能提高高纬度地区汞的氧化和沉积速率。 ⁸这些化学循环中的一个关键物质是氧化碘 (IO) 自由基，当水平足够高时，它也可能参与粒子成核事件。 ^7,9–12在此类事件中形成的粒子有可能充当云凝结核，因此可以通过影响云的辐射特性来间接影响气候。碘也是人类和许多其他动物的必需营养素，缺乏碘是导致儿童可预防的脑损伤的主要原因。 ¹³海空转移，然后是大气运输和沉​​积到陆地上，是碘进入人类食物链的重要途径。这也是从核设施（有意或无意）排放到海洋的碘放射性核素可能返回陆地环境的一条途径。

The oceans are the largest reservoir of iodine after the Earth's crust, containing a total of around 7.93 × 10¹⁰ tonnes.¹⁴ In seawater, the majority of iodine is found as one of two dissolved inorganic ions – iodide (I⁻) and iodate (IO₃⁻).¹⁵ The total amount of inorganic iodine (the sum of iodide and iodate) is close to constant across the oceans at ∼450 to 500 nM,^15–17 but the ratio of iodide to iodate varies with both geographical location and depth (see Section 3).
海洋是继地壳之后最大的碘储库，总储量约为 7.93 × 10 ¹⁰吨。 ¹⁴在海水中，大部分碘以两种溶解的无机离子之一的形式存在——碘化物 (I ⁻ ) 和碘酸根 (IO ₃ ⁻ )。 ¹⁵整个海洋中无机碘的总量（碘化物和碘酸盐的总和）接近恒定，约为 450 至 500 nM， ^15-17，但碘化物与碘酸盐的比例随地理位置和深度的不同而变化（见第 3 节） ）。

Sea-to-air exchange is the dominant source of iodine to the atmosphere^1,8 with an estimated global flux of the order of 10¹² g per year.^8,18 Until recently, fluxes of volatile organic iodine compounds (e.g. CH₃I, CH₂I₂) were thought to be the main source of iodine to the marine atmosphere (e.g.ref. 1, 4 and 11). However, it has become evident that known sources of organoiodines cannot sustain the observed concentrations of gas-phase iodine oxide,^6,19–22 and consequently there has been a resurgence of interest in the reactions of inorganic iodine compounds at the sea surface.
海空交换是大气中碘^1,8的主要来源，估计全球每年的碘通量约为 10 ¹²克。 ^8,18直到最近，挥发性有机碘化合物（例如CH ₃ I、CH ₂ I ₂ ）通量还被认为是海洋大气中碘的主要来源（例如参考文献1、4 和11 ）。然而，很明显，已知的有机碘来源无法维持观察到的气相氧化碘^6,19-22的浓度，因此人们对海面无机碘化合物的反应重新产生了兴趣。

At the air–sea interface, dissolved iodide (I⁻) reacts with gas phase ozone to liberate molecular iodine via reactions (R1) and (R2) below:^18,23,24
在海气界面，溶解的碘化物 (I ⁻ ) 与气相臭氧发生反应，通过以下反应(R1)和(R2)释放分子碘： ^18,23,24 I⁻ + O₃ + H⁺ → HOI + O₂
I ⁻ + O ₃ + H ⁺ → HOI + O ₂ (R1) HOI + I⁻ + H⁺ → I₂ + H₂O
HOI + I ⁻ + H ⁺ → I ₂ + H ₂ O (R2)

Reaction (R1) is one of a number of processes known to destroy ozone in the surface ocean,²⁵ which together are thought to be responsible for the observed atmospheric ozone deposition velocity to the oceans being 40 times greater than that predicted from physical dissolution alone.²⁶ Deposition to the sea surface is a significant ozone sink, accounting for around one third of total global ozone dry deposition flux (600–1000 Tg O₃ per year).²⁷ Estimates of the contribution of reaction (R1) to the chemical enhancement of ozone deposition range from 20%²⁸ to almost 100%.²⁵
反应(R1)是已知会破坏海洋表层臭氧的众多过程之一， ²⁵人们认为这些过程共同导致观测到的大气臭氧沉积到海洋的速度比仅通过物理溶解预测的速度快 40 倍。 ²⁶海面沉积是一个重要的臭氧汇，约占全球臭氧干沉积通量总量的三分之一（每年 600-1000 Tg O ₃ ）。 ²⁷反应(R1)对臭氧沉积化学增强的贡献估计范围从 20% ²⁸到几乎 100%。 ²⁵

The reactive iodine (HOI and I₂) released to the atmosphere as a result of reactions (R1) and (R2) is photolysed to yield iodine atoms, which in turn react with ozone in the gas phase to form iodine oxide.^1,8 This gas phase chemistry represents a catalytic loss pathway for tropospheric ozone. Carpenter et al.²⁹ recently demonstrated that reactions (R1) and (R2) could explain around 75% of the iodine oxide levels measured over the tropical Atlantic. Inclusion of these reactions in atmospheric chemistry models has subsequently yielded good agreement between observed levels of molecular iodine and iodine oxide at Cape Verde,²⁰ and reasonable agreement between modelled and observed iodine oxide levels over the eastern Pacific.³⁰
由于反应(R1)和(R2)而释放到大气中的活性碘(HOI和I ₂ )被光解产生碘原子，碘原子又与气相中的臭氧反应形成氧化碘。 ^1,8这种气相化学代表了对流层臭氧的催化损失途径。卡彭特等人。 ²⁹最近证明，反应(R1)和(R2)可以解释热带大西洋上空测量到的约 75% 的氧化碘水平。将这些反应纳入大气化学模型后，佛得角观测到的分子碘和氧化碘水平之间取得了良好的一致性， ²⁰东太平洋上空的模拟和观测到的氧化碘水平也取得了合理的一致性。 ³⁰

The strength of the reactive iodine source and the ozone deposition flux are related to sea surface iodide concentration,^24,29,31 so to estimate the significance of these processes requires an accurate representation of sea surface iodide concentrations. Iodide concentrations are not constant at the sea surface; observations in different locations vary by approximately one order of magnitude (see Section 3). Measurements of iodide are sparse compared to parameters such as salinity or nutrient concentrations, and aqueous iodine species cannot yet be detected by either remote sensing or easily automated methods. The scarcity of oceanic iodide measurements and need for a synthesis of iodine biogeochemistry relevant to the atmospheric chemistry community has been highlighted in a number of recent publications.^21,32 In the absence of comprehensive global and regional iodide data sets, sea surface iodide concentrations have instead been estimated as a function of more readily available oceanographic variables, specifically nitrate^27,32 and chlorophyll-a,^32,33 in the context of quantifying large-scale ozone deposition. Sea surface temperature has also been used as proxy for iodide concentration in order to estimate iodine emissions.³⁰
活性碘源的强度和臭氧沉降通量与海面碘化物浓度相关， ^24,29,31因此，要估计这些过程的重要性，需要准确表示海面碘化物浓度。海面的碘化物浓度并不恒定；不同地点的观测结果相差大约一个数量级（见第 3 节）。与盐度或营养物浓度等参数相比，碘化物的测量结果很少，并且还无法通过遥感或简单的自动化方法检测含水碘物质。最近的许多出版物都强调了海洋碘化物测量的稀缺性以及对与大气化学界相关的碘生物地球化学合成的需求。 ^21,32在缺乏全面的全球和区域碘化物数据集的情况下，海面碘化物浓度被估算为更容易获得的海洋学变量的函数，特别是硝酸盐^27,32和叶绿素-a, ^32,33量化大规模臭氧沉降。海面温度也被用作碘化物浓度的替代指标，以估算碘排放量。 ³⁰

Here we present a geographically extensive compilation of the available sea surface iodide measurements, including data from the literature, archived resources and new, previously unpublished data collected during five research cruises. To the best of our knowledge, this is the largest and most detailed compilation of seawater iodide measurements presented to date. We describe the large-scale distribution of iodine compounds in the surface ocean, with a focus on iodide concentrations at the sea-surface, as it is this that impacts directly on atmospheric chemistry. Relationships between iodide concentration and more easily available oceanographic variables (chlorophyll, nitrate, sea surface temperature, salinity, mixed layer depth) are evaluated as tools to predict iodide concentration.
在这里，我们提供了现有海面碘化物测量数据的地理范围广泛的汇编，包括来自文献、存档资源的数据以及在五次研究航行期间收集的新的、先前未发表的数据。据我们所知，这是迄今为止最大、最详细的海水碘化物测量数据汇编。我们描述了海洋表层碘化合物的大规模分布，重点关注海面的碘化物浓度，因为它直接影响大气化学。碘化物浓度与更容易获得的海洋变量（叶绿素、硝酸盐、海面温度、盐度、混合层深度）之间的关系被评估为预测碘化物浓度的工具。

2. Compilation of the iodide data set
2.碘化物数据集的编译

A large number of studies have examined the distribution of iodine compounds in the oceans over local, regional and basin wide scales. The results of these studies have been digitised where possible and supplemented by data kindly supplied directly by other investigators, data archives, and unpublished measurements made by the authors during five different field campaigns (see Table 1 for a list of data sets). Due to the small total number of measurements, the compiled data set has not been filtered according to season or time of day of sampling. The potential for temporal variation in dissolved iodine speciation is discussed in Section 3.2. A total of 925 surface data points collected from 44 sources have been collated into a single data set. The locations of data points included in the surface compilation are shown in Fig. 1.
大量研究调查了局部、区域和盆地范围内海洋中碘化合物的分布。这些研究的结果已尽可能数字化，并由其他研究人员直接提供的数据、数据档案以及作者在五次不同的实地活动中进行的未发表的测量数据进行补充（数据集列表见表 1 ）。由于测量总数较少，编制的数据集尚未根据季节或采样时间进行过滤。溶解碘形态随时间变化的可能性在 3.2 节中讨论。从 44 个来源收集的总共 925 个表面数据点已整理成一个数据集。表面编译中包含的数据点的位置如图1所示。

Surface is here defined as the upper 20 m of the water column. This depth was selected as a compromise between maximising the number of data points included and attempting to represent concentrations at the actual surface accurately. At the air–sea interface itself, it has been suggested that iodide concentration may be enhanced or depleted compared to the bulk surface seawater immediately below; this is discussed in Section 3.5. Iodide measurements made within a few millimetres of the ocean surface are extremely rare, so it was necessary to use bulk surface water measurements in this compilation. On ship-based campaigns, ‘surface’ water is usually collected from an underway pumped seawater inlet (typically at a depth of around 6 m on a 100 m length research ship), and/or sampling bottles mounted on a CTD rosette and closed within a few metres of the sea surface, but during some field campaigns (e.g. winter samples in the Antarctic⁷³), only data from 15 m depth was available. In most cases, the water column is thought to be sufficiently homogenous between 0 and 20 m that this choice of depth can be assumed to be representative of concentrations in the top few metres of the water column (see Section 3.4 for a description of the changes in iodine speciation with depth).
此处表面定义为水柱上部 20 m。选择该深度是为了最大化所包含的数据点数量和尝试准确表示实际表面的浓度之间的折衷。在空气-海洋界面本身，有人认为与紧邻下方的大量表层海水相比，碘化物浓度可能会增加或减少；这将在 3.5 节中讨论。在海洋表面几毫米内进行的碘化物测量极为罕见，因此在本次汇编中有必要使用大量地表水测量。在基于船的活动中，“地表”水通常从航行中泵送的海水入口（通常在 100 m 长的研究船上位于约 6 m 的深度）和/或安装在 CTD 花环上并封闭在内部的采样瓶收集。数米的海面，但在一些野外活动期间（例如南极洲的冬季样本⁷³ ），只能获得15 m 深度的数据。在大多数情况下，水柱被认为在 0 到 20 m 之间足够均匀，因此可以假设这种深度选择代表了水柱顶部几米的浓度（有关变化的描述，请参见第 3.4 节）碘形态与深度）。

A variety of different methods for the determination of iodine species in seawater have been reported in the literature. Details of the methods used in each study included in our compilation are summarised in Table 1. For all unpublished data included here, iodide was measured using cathodic stripping square wave voltammetry (CSSWV),^69,75 following protocols described in Chance et al., 2010.⁷³ Direct measurements of iodide are most commonly made by CSSWV, which is specific for the iodide ion. Other direct methods of iodide determination include ion chromatography,⁴⁹ capillary electrophoresis⁶³ and flow through electrodes.⁵⁵ Precision estimates for direct methods are 4–10% for CSSWV,^69,73,75 2% for ion chromatography,⁴⁹ 3% for capillary electrophoresis⁶³ and 5% for the flow through electrode method.⁵⁴ Other studies do not measure iodide directly, but infer it as the difference between total dissolved iodine and iodate concentrations, where these parameters have usually been determined by spectrophotometric^47,70 or polarographic^52,68 techniques. The precision of these methods is less than 5% for each species, and sometimes reported as better than 1%;^47,52,68,70 propagation of errors leads to an uncertainty of between <6% to ∼28% for an iodide concentration of 100 nM calculated by difference, and will increase as iodide concentration decreases. Depending on the analytical methods used, the difference approach may result in a small over-estimation of iodide, due to the presence of an unquantified organic iodine fraction with variable reactivity towards the total iodine method. In the open ocean, the dissolved organic iodine fraction is very small (less than 10%)^15,58,76 and only a portion of this may cause analytical interference, so this effect is negligible. However, in coastal waters where organic iodine may be high (40 to 80% e.g.ref. 76–79) it could become significant. Generally, the analytical uncertainties for the iodine species are small compared to the observed environmental gradients. In some campaigns included in our compilation (e.g. Truesdale et al., 2000 (ref. 70)), iodide concentrations were not reported, and so we have calculated them by difference, using total iodine and iodate concentrations taken from the relevant publication.
文献中报道了多种不同的测定海水中碘形态的方法。表 1总结了我们汇编中包含的每项研究中使用的方法的详细信息。对于此处包含的所有未发表的数据，碘化物是使用阴极溶出方波伏安法 (CSSWV) 测量的， ^69,75遵循 Chance等人中描述的方案。 ，2010。 ⁷³碘离子的直接测量最常见的是 CSSWV，它专门针对碘离子。其他直接测定碘化物的方法包括离子色谱法、 ⁴⁹毛细管电泳法⁶³和流过电极法。 ⁵⁵ CSSWV 直接法的精度估计为 4–10%，离子色谱法为^69,73,75 2%，毛细管电泳法为⁴⁹ 3% ⁶³ ，流通电极法为 5%。 ⁵⁴其他研究并不直接测量碘化物，而是将其推断为总溶解碘和碘酸盐浓度之间的差异，其中这些参数通常通过分光光度法^47,70或极谱法^52,68技术确定。对于每个物种，这些方法的精确度低于 5%，有时报告优于 1%； ^47,52,68,70对于通过差值计算的 100 nM 碘化物浓度，误差传播导致不确定度在 <6% 至 ∼28% 之间，并且随着碘化物浓度降低而增加。 根据所使用的分析方法，差异法可能会导致碘化物的估算略有高估，因为存在未定量的有机碘部分，其对总碘方法的反应性不同。在公海中，溶解的有机碘含量非常小（小于 10%） ^15,58,76 ，只有其中一部分可能会造成分析干扰，因此这种影响可以忽略不计。然而，在有机碘含量可能较高的沿海水域（40% 至 80% ，例如参考文献 76-79 ），其含量可能会变得很高。一般来说，与观察到的环境梯度相比，碘物质的分析不确定性很小。在我们的汇编中包含的一些活动中（例如Truesdale等人，2000年（参考文献70 ）），没有报告碘化物浓度，因此我们使用从相关出版物中获取的总碘和碘酸盐浓度通过差值计算它们。

3. The distribution of iodine compounds in seawater
3、海水中碘化合物的分布

3.1. Iodide and iodate concentrations at the sea surface
3.1.海面碘化物和碘酸盐浓度

The 925 surface iodide concentrations in our compilation are shown in Fig. 2A and 3, and the corresponding iodate concentrations are shown in Fig. 2B. Fig. 2 was produced using the DIVA interpolation function in the Ocean Data View software.⁸⁰ The estimated uncertainties for each iodide measurement are shown in Fig. S1 (in the ESI†). Observed iodide concentrations range from undetectable (limits of detection were not always reported, but are typically around 1 nM) to 700 nM, with a median value of 77 nM and interquartile range of 28 to 140 nM (Fig. 4). Although coverage of iodide measurements is sparse compared to parameters such as nutrients and pigments, sufficient data exists to be able to describe the large scale distribution, which shows a clear and systematic spatial gradient. In general, highest iodide concentrations (greater than 100 nM) are observed at low latitudes and lower iodide concentrations (less than 50 nM) at latitudes greater than about 40 degrees north or south (Fig. 2A and 3). Iodide concentrations were significantly correlated with absolute latitude (Tables 2 and 3). The increase in iodide concentrations with decreasing latitude is particularly pronounced between about 50° and 20°, while at tropical latitudes there is a slight indication of a levelling, or even a dip, in iodide concentrations moving toward the equator (Fig. 3). Iodate has an approximately opposite distribution to iodide (Fig. 2B), with highest levels typically observed at high latitudes. This large-scale latitudinal gradient in iodine speciation has been demonstrated during transects of the Atlantic^17,53 and Pacific.⁶⁷
我们编制的925个表面碘化物浓度如图2A和图3所示，相应的碘酸盐浓度如图2B所示。图2是使用Ocean Data View软件中的DIVA插值功能生成的。 ⁸⁰每个碘化物测量的估计不确定度如图 S1 所示（在 ESI †中）。观察到的碘化物浓度范围从不可检测（检测限并不总是报告，但通常在 1 nM 左右）到 700 nM，中值为 77 nM，四分位数范围为 28 至 140 nM（图 4 ）。尽管与营养素和色素等参数相比，碘化物测量的覆盖范围很稀疏，但存在足够的数据能够描述大规模分布，显示出清晰且系统的空间梯度。一般来说，在低纬度观察到最高的碘化物浓度（大于100nM），而在北纬或南纬大于约40度的地区观察到较低的碘化物浓度（小于50nM）（图2A和3 ）。碘化物浓度与绝对纬度显着相关（表2和表3 ）。随着纬度的降低，碘化物浓度的增加在大约 50° 至 20° 之间尤其明显，而在热带纬度，有轻微迹象表明碘化物浓度向赤道移动趋于平稳，甚至下降（图 3 ）。碘酸盐的分布与碘化物大致相反（图2B ），通常在高纬度地区观察到最高水平。 这种大规模的碘形态纬度梯度已在大西洋^17,53和太平洋的横断面中得到证实。⁶⁷

A number of studies have observed a decrease in the proportion of dissolved inorganic iodine present as iodate as the coast is approached,^46,47,52 and it has been suggested that reduction of iodate to iodide may be particularly effective in coastal waters.^50,51,81 We note that the highest iodide concentrations in our compilation often occur near coastlines (Fig. 2). In order to separate the effects of latitude and coastal proximity on iodide distribution, the data set was sub-divided into coastal and open ocean regions, where coastal data points were defined as those falling into coastal biogeochemical provinces,⁸² plus Bermuda inshore waters which fall within an open ocean province (NAST-W) but are on the Bermuda platform.⁴⁷ Exceptions to the latitudinal trend in iodide concentrations occur almost exclusively in coastal waters (Fig. 3). For a given latitude, iodide concentrations appear to have higher variability in coastal waters compared to the open ocean (Fig. 3). This may in part reflect a sampling bias, in that coastal waters may have been sampled at more different times of year (including time series studies) than open ocean locations, which may have only been visited during a single research cruise. Considering all latitudes, there is a modest difference in the spread of data between the open ocean and coastal sub-sets. Coastal waters have a larger range than open ocean waters, but this is due to the occurrence of a very high outlier with an iodide concentration of 700 nM (Fig. 4A). This sample was collected in the Skaggerrak, and had a salinity of 27.7,³⁵ so may be reasonably considered an unusual case. Excluding outliers, the range of coastal samples is 53 nM greater than the open ocean samples and the interquartile range is 20 nM greater (Fig. 4A).
许多研究观察到，随着靠近海岸，以碘酸盐形式存在的溶解无机碘的比例下降， ^46,47,52 ，并且有人建议，将碘酸盐还原为碘化物在沿海水域可能特别有效。 ^50,51,81我们注意到，我们编制的碘化物浓度最高的区域通常出现在海岸线附近（图 2 ）。为了区分纬度和沿海距离对碘化物分布的影响，数据集被细分为沿海和公海区域，其中沿海数据点被定义为属于沿海生物地球化学省的数据点， ⁸²加上百慕大近海水域的数据点。位于开放海洋省（NAST-W）内，但位于百慕大平台上。 ⁴⁷碘化物浓度纬度趋势的例外情况几乎全部发生在沿海水域（图 3 ）。对于给定的纬度，与公海相比，沿海水域的碘化物浓度似乎具有更高的变异性（图3 ）。这可能部分反映了采样偏差，因为与公海地点相比，沿海水域可能在一年中更多的不同时间（包括时间序列研究）进行了采样，而公海地点可能仅在一次研究巡航期间进行了访问。考虑到所有纬度，公海和沿海子集之间的数据分布存在适度差异。沿海水域的范围比公海水域更大，但这是由于出现了碘化物浓度为 700 nM 的非常高的异常值（图 4A ）。该样本是在 Skaggerrak 采集的，盐度为 27。7, ³⁵因此可以合理地视为异常情况。排除异常值，沿海样本的范围比公海样本大53 nM，四分位距大20 nM（图4A ）。

Further sub-division of the open ocean data-set into arbitrary latitudinal bands (0–23.4°; 23.5–35.5°, 36–60° and >60° north or south) also demonstrates the trend for decreasing iodide concentration with increasing latitude (Fig. 4B), although there is overlap between the range of the data, particularly at low latitudes. Interestingly, iodide concentrations at the highest latitudes (>60°) appear to be a little higher than those in more temperate regions (35–60°) with median values of 33 and 18 nM respectively (Fig. 4B).
将公海数据集进一步细分为任意纬度带（0–23.4°；23.5–35.5°、36–60°和>60°北或南）也表明碘化物浓度随着纬度增加而降低的趋势（图 4B ），尽管数据范围之间存在重叠，特别是在低纬度地区。有趣的是，最高纬度（>60°）的碘化物浓度似乎略高于温带地区（35-60°）的碘化物浓度，中值分别为33和18 nM（图4B ）。

3.2. Changes in iodine speciation with time
3.2.碘形态随时间的变化

3.2.1. Rates of iodine redox transformations in seawater
3.2.1.海水中碘氧化还原转化率

The time scales for changes in dissolved iodine speciation in the surface ocean are quite poorly constrained. This is in part due to the scarcity of time series studies, and the need to account for external forcing such as advection and vertical mixing, as well as in situ rates of change in a parcel of water. In general, the reduction of iodate to iodide is considered to occur more rapidly than the reverse reaction.¹⁵Net rates of iodide accumulation (and iodate depletion) of 0.27 to 0.55 nM per day have been observed in the surface ocean over 78 days,⁷³ but other studies have found no discernible net change over similar time periods.³⁷ Under low oxygen conditions, much faster rates have been observed (∼50 nM h⁻¹;⁸³), but these are not relevant to surface open ocean conditions. The oxidation of iodide to iodate in oxygenated seawater is slow;^15,84 this kinetic barrier allows iodide to persist alongside iodate in the surface ocean, despite it being thermodynamically less stable,⁸⁵ and hence it is termed metastable. Estimates of the oceanic lifetime of iodide with respect to oxidation range from 40 years (∼4 nM per year)⁶¹ to six months or less (with rates of 300 nM per year;⁸⁶ 270–560 nM per year;⁴¹ and 670 nM per year;⁸⁷ reported). These latter oxidation rates are too fast to be explained by suggested abiotic pathways,^15,84,88,89 so a biologically mediated route may need to be invoked, for example it has recently been suggested that iodide oxidation is associated with nitrification processes.⁸⁷ Rates of change must be considered when searching for a suitable proxy for iodide concentration – a proxy which changes on an hourly or daily basis is likely to vary too rapidly to reflect significant changes in iodide concentration, while those that vary on a seasonal timescale may be more appropriate, since iodide production and loss processes appear to operate over timescales of weeks to months.
表层海洋中溶解的碘形态变化的时间尺度受到的限制非常少。这部分是由于时间序列研究的缺乏，以及需要考虑平流和垂直混合等外部强迫，以及一块水的原位变化率。一般来说，碘酸盐还原成碘化物被认为比逆反应发生得更快。 ¹⁵在 78 天的时间里，在表层海洋中观察到每天 0.27 至 0.55 nM 的碘化物累积（和碘酸盐消耗）净速率， ⁷³但其他研究发现在相似的时间段内没有明显的净变化。 ³⁷在低氧条件下，观察到更快的速率（∼50 nM h ^-1 ; ⁸³ ），但这些与表面开放海洋条件无关。碘化物在含氧海水中氧化成碘酸盐的速度很慢； ^15,84这种动力势垒允许碘化物与碘酸盐一起存在于海洋表层，尽管它在热力学上不太稳定， ⁸⁵因此被称为亚稳态。碘化物在海洋中的氧化寿命估计范围为 40 年（每年约 4 nM） ⁶¹至 6 个月或更短（每年 300 nM；每年⁸⁶ 270–560 nM；每年⁴¹和 670 nM）。年； ⁸⁷报道）。 后者的氧化速率太快，无法通过建议的非生物途径来解释， ^15,84,88,89因此可能需要调用生物介导的途径，例如最近有人提出碘化物氧化与硝化过程相关。 ⁸⁷在寻找合适的碘化物浓度替代值时，必须考虑变化率——每小时或每天变化的替代值可能变化太快，无法反映碘化物浓度的显着变化，而那些随季节时间尺度变化的替代值可能会变化。更合适，因为碘化物的生产和损失过程似乎需要数周至数月的时间尺度。

3.2.2. Seasonal variation
3.2.2.季节变化

The surface ocean is subject to seasonal cycles in mixing and biological production, which can in turn cause seasonal changes in concentrations of biogeochemically active chemical species.⁹⁰ Very generally, vertical mixing of the water column tends to be deeper in winter, while in summer stratification causes isolation of a surface layer. In spring, increasing light levels and the onset of stratification drive an increase in phytoplankton growth (the ‘spring bloom’), which consumes nutrients and may be associated with an increase in levels of biogenic compounds. Stratification prevents the resupply of nutrients by upward mixing, so eventually nutrients in the surface ocean may become exhausted, causing a decline in phytoplankton growth in the summer.
表层海洋受到混合和生物生产的季节性循环的影响，这反过来又会导致生物地球化学活性化学物质浓度的季节性变化。 ⁹⁰一般来说，冬季水柱的垂直混合往往更深，而夏季分层会导致表层隔离。在春季，光照水平的增加和分层的开始会促进浮游植物的生长（“春季水华”），从而消耗营养，并可能与生物化合物水平的增加有关。分层阻止了通过向上混合来补充营养物质，因此最终海洋表层的营养物质可能会耗尽，导致夏季浮游植物生长下降。

There is evidence both for and against a seasonal cycle in surface iodide (and iodate) concentrations. The spikes in iodide concentrations at 23°N, 32°N, 43°N and 67°S (Fig. 3) are the result of temporal variations observed during time series studies at stations in the tropical Pacific,⁴¹ the Atlantic,^41,47 the Mediterranean^43,44 and the western Antarctic peninsula,⁷³ respectively. Where these changes follow a discernible seasonal cycle, surface iodide concentrations increase (and iodate concentrations decrease) over periods of stratification in summer, while minimum iodide (and maximum iodate) concentrations are observed during winter when vertical mixing is greatest.^43,47,73 Changes in iodine speciation have not necessarily been in step with primary productivity,⁴⁷ but have sometimes indicated a loss of iodate associated with the onset of phytoplankton growth in spring, and a concurrent or delayed increase in iodide concentration.^41,51,73 Meanwhile, other studies have not found any evidence for seasonal changes in iodine speciation.^35,38,46,70
有证据支持和反对表面碘化物（和碘酸盐）浓度的季节性周期。 23°N、32°N、43°N 和 67°S 处的碘化物浓度峰值（图 3 ）是热带太平洋、 ⁴¹大西洋、 ^{41、 47}地中海^43，44和南极半岛西部分别⁷³ 。在这些变化遵循明显的季节周期的情况下，表面碘化物浓度在夏季分层期间增加（而碘酸盐浓度降低），而在垂直混合最大的冬季观察到最低碘化物（和最大碘酸盐）浓度。 ^43,47,73碘形态的变化不一定与初级生产力同步， ⁴⁷但有时表明与春季浮游植物生长开始相关的碘酸盐损失，以及碘化物浓度的同时或延迟增加。 ^41,51,73同时，其他研究尚未发现碘形态季节性变化的任何证据。 ^35,38,46,70

Given the possibility of seasonal variation in iodine speciation, it would be desirable to create a climatology that is filtered by season; unfortunately, insufficient data is available to attempt this at present and the possibility of seasonal iodide variations should be considered as a source of uncertainty when modelling iodine chemistry at the sea surface. Note that the amplitudes of any unaccounted for seasonal variations in iodide concentration in the data compilation are not sufficient to mask the spatial patterns in iodide distribution described in Section 3.1, and the same general trends remain even when the data is divided by season (see Fig. S2a–d in the ESI†). Furthermore, at the time series stations noted above, seasonal maxima and minima are lower at higher latitudes (Fig. 3).
考虑到碘形态存在季节性变化的可能性，建立按季节过滤的气候学是可取的；不幸的是，目前没有足够的数据来尝试这一点，并且在对海面的碘化学进行建模时，应将季节性碘化物变化的可能性视为不确定性的来源。请注意，数据汇编中任何未考虑的碘化物浓度季节性变化的幅度不足以掩盖第 3.1 节中描述的碘化物分布的空间模式，即使数据按季节划分，相同的总体趋势仍然存在（见图 1）。 ESI 中的